String Diagram Tutorial

by Aaron Lauda


    \[
    \xy
    (0,0)*{f};
    (0,0)*\xycircle(2.65,2.65){-}="f";
    (0,10)**\dir{-} ?(.5)*\dir{<}+(3,0)*{\scriptstyle x};
    "f";(0,-10)**\dir{-} ?(.75)*\dir{>}+(3,0)*{\scriptstyle y};
    \endxy
    \]
Here I am using the \xycircle command to create a circle in this diagram. There are other ways to make circles but I kept having trouble with the pdf version of the document so now I just use this one. I simply gave the circle the name f and made directionals coming out both ends. The downside with making the circles this way is that I had to include the extra command to stick the label inside the circle. The nice thing about using \xycircle is that you can adjust the size of the circle to accomodate any size label. The +(3,0)*{\scriptstyle y} included after the directional is a quick way to stick on labels. Sometimes I have trouble getting labels to line up properly when I label things in this way, so I ofter just stick the label in using something like \(5,5)*{\scriptstyle y}.


    \xy
    (-5,0)*{f};
    (-5,12)*{}; (-5,0)*\xycircle(2.65,2.65){-}="1_x"; **\dir{-}
    ?(.5)*\dir{<}+(3,0)*{\scriptstyle x}; "1_x";(-5,-12)*{}; **\dir{-}
    ?(.4)*\dir{<}+(3,0)*{\scriptstyle y}; (5,12)*{};
    (5,0)*\xycircle(2.65,2.65){-}="1_x"; **\dir{-}
    ?(.5)*\dir{<}+(3,0)*{\scriptstyle x'}; "1_x";(5,-12)*{}; **\dir{-}
    ?(.4)*\dir{<}+(3,0)*{\scriptstyle y'}; (5,0)*{g};
    \endxy
    \qquad = \qquad \xy (0,12)*{};
    (0,0)*\xycircle(2.95,2.95){-}="1_x"; **\dir{-}
    ?(.5)*\dir{<}+(4,3)*{\scriptstyle x \ten x'}; "1_x";(0,-12)*{};
    **\dir{-} ?(.4)*\dir{<}+(4,0)*{\scriptstyle y \ten y'}; (0,0)*{
    \scriptstyle f \ten g};
    \endxy


    \xy (0,12)*{};(0,-12)*{}; **\dir{-}
    ?(.47)*\dir{<}+(3,1)*{\scriptstyle x}
    \endxy
    \qquad = \qquad \xy (0,12)*{};
    (0,0)*\xycircle(2.65,2.65){-}="1_x"; **\dir{-}
    ?(.5)*\dir{<}+(3,0)*{\scriptstyle x}; "1_x";(0,-12)*{}; **\dir{-}
    ?(.4)*\dir{<}+(3,0)*{\scriptstyle x}; (0,0)*{1_x};
    \endxy


    \xy
    (0,10)*{};
    (0,-10)*{}
    **\dir{-}?(.54)*\dir{>}+(-2.5,1)*{\xb};
    \endxy
    \qquad = \qquad
    \xy
    (0,10)*{};
    (0,-10)*{}
    **\dir{-}?(.45)*\dir{<}+(2.5,-1)*{x};
    \endxy


    \xy
    (-6,0)*{};
    (6,0)*{};
    **\crv{(0,18)} ?(.16)*\dir{>} ?(.9)*\dir{>};
    (1,11)*{\scriptstyle i_{x}};
    \endxy


    \xy
    (-6,4)*{};(6,4)*{};
    **\crv{(0,-12)}
    ?(.20)*\dir{>}+(2,-1)
    ?(.89)*\dir{>}+(-2,-1);
    (1,-6)*{\scriptstyle e_{x}};
    \endxy


    \xy
    (0,-10)*++{}="g";
    (10,0)*{}="mid";
    **\crv{(5,20)} ?(.83)*\dir{>};
    (6.5,10)*{\scriptstyle i_{x}};
    (20,10)*++{}="f";
    "f";"mid"; **\crv{(15,-20)} ?(0)*\dir{<} ?(.76)*\dir{<};
    (15.5,-10)*{\scriptstyle e_{x}};
    \endxy
    \quad = \quad \xy (0,10)*{};(0,-10)*{}; **\dir{-}
    ?(.47)*\dir{<}+(3,1)*{\scriptstyle x}
    \endxy
    \qquad \qquad \xy
    (0,10)*++{}="g";
    (10,0)*{}="mid";
    **\crv{(5,-20)} ?(.02)*\dir{>} ?(.83)*\dir{>};
    (6,-10)*{\scriptstyle e_{x}};
    (20,-10)*++{}="f";
    "f";"mid"; **\crv{(15,20)} ?(.78)*\dir{<};
    (15,10)*{\scriptstyle i_{x}};
    \endxy
    \quad = \quad \xy (0,10)*{};(0,-10)*{}; **\dir{-}
    ?(.53)*\dir{>}+(3,1)*{\scriptstyle x}
    \endxy


    \xy
    (-6,0)*{};
    (6,0)*{};
    **\crv{(0,18)} ?(.16)*\dir{>} ?(.9)*\dir{>};
    (1,11)*{};
    \endxy


    \xy
    (-6,4)*{};(6,4)*{};
    **\crv{(0,-12)}
    ?(.20)*\dir{>}+(2,-1)
    ?(.89)*\dir{>}+(-2,-1);
    (1,-6)*{};
    \endxy


    \xy
    (0,-10)*++{}="g";
    (10,0)*{}="mid";
    **\crv{(5,20)} ?(.83)*\dir{>};
    (6.5,10)*{};
    (20,10)*++{}="f";
    "f";"mid"; **\crv{(15,-20)} ?(0)*\dir{<} ?(.76)*\dir{<};
    (15.5,-10)*{};
    \endxy
    \quad = \quad \xy (0,10)*{};(0,-10)*{}; **\dir{-}
    ?(.47)*\dir{<}+(3,1)*{}
    \endxy
    \qquad \qquad \xy
    (0,10)*++{}="g";
    (10,0)*{}="mid";
    **\crv{(5,-20)} ?(.02)*\dir{>} ?(.83)*\dir{>};
    (20,-10)*++{}="f";
    "f";"mid"; **\crv{(15,20)} ?(.78)*\dir{<};
    (15,10)*{};
    \endxy
    \quad = \quad \xy (0,10)*{};(0,-10)*{}; **\dir{-}
    ?(.53)*\dir{>}+(3,1)*{}
    \endxy


    \xy
    (-6,4)*{};(6,4)*{};
    **\crv{(0,-12)}
    ?(.1)*\dir{<}+(2,-1)
    ?(.80)*\dir{<}+(-2,-1);
    (1,-6)*{};
    \endxy


    \xy
    (-6,0)*{};
    (6,0)*{};
    **\crv{(0,18)}
    ?(.10)*\dir{<}
    ?(.85)*\dir{<};
    (1,11)*{};
    \endxy


    \xy
    (6,0)*{}="1";
    (-6,0)*{}="2";
    "1";"2" **\crv{(7,15)&(-7,15)}
    ?(0)*\dir{>} ;
    "2";"1" **\crv{ (-7,-15)& (7,-15)}
    ?(.05)*\dir{>} ;
    \endxy
    \quad = \quad \qquad \qquad \qquad \qquad \qquad \xy
    (6,0)*{}="1";
    (-6,0)*{}="2";
    "2";"1" **\crv{(-7,15)&(7,15)}
    ?(0)*\dir{>} ;
    "1";"2" **\crv{(7,-15) & (-7,-15)}
    ?(.05)*\dir{>} ;
    \endxy
    \quad = \quad \qquad \qquad


    \xy
    (-6,10)*{};
    (6,10)*{};
    **\crv{(0,-8)} ?(.22)*\dir{>} ?(.87)*\dir{>};
    (6,-10)*{};
    (-6,-10)*{};
    **\crv{(0,8)} ?(.20)*\dir{>} ?(.87)*\dir{>};
    \endxy
    \quad = \quad \xy (-3,-10)*{};(-3,10)**\dir{-} ?(.57)*\dir{>};
    (3,10)*{};(3,-10)**\dir{-} ?(.57)*\dir{>};
    \endxy
    \quad \qquad \qquad \qquad \quad \xy
    (6,10)*{};
    (-6,10)*{};
    **\crv{(0,-8)} ?(.22)*\dir{>} ?(.87)*\dir{>};
    (-6,-10)*{};
    (6,-10)*{};
    **\crv{(0,8)} ?(.20)*\dir{>} ?(.87)*\dir{>};
    \endxy
    \quad = \quad \xy (-3,10)*{};(-3,-10)**\dir{-} ?(.57)*\dir{>};
    (3,-10)*{};(3,10)**\dir{-} ?(.57)*\dir{>};
    \endxy


    \xy
    (0,-10)*++{}="g";
    (10,0)*{}="mid";
    **\crv{(5,20)} ?(.8)*\dir{<};
    (6.5,10)*{};
    (20,10)*++{}="f";
    "f";"mid"; **\crv{(15,-20)} ?(.08)*\dir{>} ?(.8)*\dir{>};
    (15.5,-10)*{};
    \endxy
    \quad = \quad \xy (0,10)*{};(0,-10)*{}; **\dir{-}
    ?(.53)*\dir{>}+(3,1)*{}
    \endxy
    \qquad \qquad \xy
    (0,10)*++{}="g";
    (10,0)*{}="mid";
    **\crv{(5,-20)} ?(.02)*\dir{<} ?(.75)*\dir{<};
    (6,-10)*{};
    (20,-10)*++{}="f";
    "f";"mid"; **\crv{(15,20)} ?(.83)*\dir{>};
    (15,10)*{};
    \endxy
    \quad = \quad \xy (0,10)*{};(0,-10)*{}; **\dir{-}
    ?(.47)*\dir{<}+(3,1)*{}
    \endxy


    \xy
    (-6,4)*{};(6,4)*{};
    **\crv{(0,-12)}
    ?(.20)*\dir{>}+(-3,-5)*{\scriptstyle e_x};
    ?(.85)*\dir{>}+(-2,-1);

    \endxy
    \quad \xy
    (6,-4)*{}; (-6,-4)*{};
    **\crv{(0,12)}
    ?(.20)*\dir{>}+(5,5)*{\scriptstyle e_y^{-1}};
    ?(.85)*\dir{>}+(-2,1);
    \endxy
    \quad = \quad \xy
    (-6,14)*{};
    (6,14)*{};
    **\crv{(0,-4)} ?(.22)*\dir{>} ?(.87)*\dir{>};
    (6,-14)*{};
    (-6,-14)*{};
    **\crv{(0,4)} ?(.20)*\dir{>} ?(.87)*\dir{>};
    (0,3)*{\scriptstyle e_x};
    (1,-3)*{\scriptstyle e_y^{-1}};
    \endxy


    \xy (-6,-8)*{}="1E"; (-6,0)*{}="1"; (0,0)*{}="2"; (6,0)*{}="3";
    (6,8)*{}="3B";
    "2";"1" **\crv{(0,10)& (-6,10)}
    ?(.03)*\dir{>} ?(1)*\dir{>};
    "3";"2" **\crv{(6,-10)& (0,-10)}
    ?(.03)*\dir{>} ;
    "1";"1E" **\dir{-};
    "3B";"3" **\dir{-};
    \endxy
    \qquad = \xy (-6,8)*{}; (0,8)*{}; (0,-8)*{}; **\dir{-}
    ?(.47)*\dir{<}; (6,-8)*{};
    \endxy


    \xy (-6,8)*{}="1E"; (-6,0)*{}="1"; (0,0)*{}="2"; (6,0)*{}="3";
    (6,-8)*{}="3B";
    "2";"1" **\crv{(0,-10)& (-6,-10)}
    ?(.03)*\dir{>} ?(1)*\dir{>};
    "3";"2" **\crv{(6,10)& (0,10)}
    ?(.03)*\dir{>} ;
    "1";"1E" **\dir{-};
    "3B";"3" **\dir{-};
    \endxy
    \qquad = \qquad \xy (-6,8)*{}="1E"; (-6,0)*{}="1"; (0,0)*{}="2";
    (6,0)*{}="3"; (6,-8)*{}="3B";
    "2";"1" **\crv{(0,-10)& (-6,-10)}
    ?(.03)*\dir{>} ?(1)*\dir{>};
    "3";"2" **\crv{(6,10)& (0,10)}
    ?(.03)*\dir{>} ;
    "1";"1E" **\dir{-};
    "3B";"3" **\dir{-};
    (12,4)*{}="1";
    (12,-4)*{}="A";
    (18,-4)*{}="B";
    (18,4)*{}="B'";
    "B'";"1" **\crv{(18,10)& (12,10)};
    "A";"B" **\crv{(12,-10)&(18,-10)};
    "B";"B'" **\dir{-} ?(.60)*\dir{>};
    "1";"A" **\dir{-}; ?(.57)*\dir{>};
    \endxy


    \xy (-6,0)*{}="1E"; (6,0)*{}="3B";
    \endxy
    \qquad = \qquad \xy (-6,8)*{}="1E"; (-6,0)*{}="1"; (0,0)*{}="2";
    (6,0)*{}="3"; (6,-8)*{}="3B";
    "2";"1" **\crv{(0,-10)& (-6,-10)}
    ?(.03)*\dir{>} ?(1)*\dir{>};
    "3";"2" **\crv{(6,10)& (0,10)};
    "1";"1E" **\dir{-};
    "3B";"3" **\dir{-};
    (12,4)*{}="1";
    (12,-4)*{}="A";
    (18,-4)*{}="B";
    (18,4)*{}="B'";
    "B'";"1" **\crv{(18,10)& (12,10)};
    "A";"B" **\crv{(12,-10)&(18,-10)};
    "B";"B'" **\dir{-} ?(.60)*\dir{>};
    "1";"A" **\dir{-};
    (6,4)*{}="D1";
    (12,4)*{}="D2";
    (6,-4)*{}="F1";
    (12,-4)*{}="F2";
    "D1";"D2" **\crv{~*=<2pt>{.}(6,0)&(12,0)};
    "F1";"F2" **\crv{~*=<2pt>{.}(6,0)&(12,0)};
    \endxy


    \xy (-6,0)*{}="1E"; (6,0)*{}="3B";
    \endxy
    \qquad = \qquad \xy (-6,8)*{}="1E"; (-6,0)*{}="1"; (0,0)*{}="2";
    (6,4)*{}="3"; (6,-8)*{}="3B";
    "2";"1" **\crv{(0,-10)& (-6,-10)}
    ?(.03)*\dir{>} ?(1)*\dir{>};
    "3";"2" **\crv{(6,10)& (-1,12)} ?(.05)*\dir{>};
    "1";"1E" **\dir{-};
    (12,4)*{}="1";
    (12,-4)*{}="A";
    (18,-4)*{}="B";
    (18,4)*{}="B'";
    "B'";"1" **\crv{(18,10)& (12,10)};
    "A";"B" **\crv{(12,-10)&(18,-10)} ?(.07)*\dir{>};
    "B";"B'" **\dir{-} ?(.60)*\dir{>};
    (6,4)*{}="D1";
    (12,4)*{}="D2";
    (6,-4)*{}="F1";
    (12,-4)*{}="F2";
    "D1";"D2" **\crv{(6,0)&(12,0)} ?(1)*\dir{<};
    "F1";"F2" **\crv{(6,0)&(12,0)}
    ?(.03)*\dir{>};
    "3B";"F1" **\dir{-};
    \endxy


    \xy (-6,0)*{}="1E"; (6,0)*{}="3B";
    \endxy
    \qquad = \qquad \xy (-6,8)*{}="1E"; (-6,0)*{}="1"; (0,0)*{}="2";
    (6,4)*{}="3"; (6,-8)*{}="3B";
    "2";"1" **\crv{(0,-10)& (-6,-10)}
    ?(.03)*\dir{>} ?(1)*\dir{>};
    "3";"2" **\crv{(6,10)& (-1,12)} ?(.05)*\dir{>};
    "1";"1E" **\dir{-};
    (12,4)*{}="1";
    (12,-4)*{}="A";
    (18,-4)*{}="B";
    (18,4)*{}="B'";
    "B'";"1" **\crv{(18,10)& (12,10)};
    "A";"B" **\crv{(12,-10)&(18,-10)} ?(.07)*\dir{>};
    "B";"B'" **\dir{-} ?(.60)*\dir{>};
    (6,4)*{}="D1";
    (12,4)*{}="D2";
    (6,-4)*{}="F1";
    (12,-4)*{}="F2";
    "D1";"D2" **\crv{(6,0)&(12,0)} ?(1)*\dir{<};
    "F1";"F2" **\crv{(6,0)&(12,0)}
    ?(.03)*\dir{>};
    "3B";"F1" **\dir{-};
    (-3,-3)*{}="X";
    (9,-6)*{}="XX";
    "X";"XX" **\dir{--};
    \endxy


    \xy (-6,0)*{}="1E"; (6,0)*{}="3B";
    \endxy
    \qquad = \qquad \xy (-6,8)*{}="1E"; (-6,4)*{}="1"; (0,4)*{}="2";
    (6,4)*{}="3"; (-6,-8)*{}="3B";
    "2";"1" **\crv{(0,0)& (-6,0)};
    ?(.0)*\dir{>};
    "3";"2" **\crv{(6,10)& (-1,12)} ?(.05)*\dir{>};
    "1";"1E" **\dir{-}; ?(.25)*\dir{>};
    (12,4)*{}="1";
    (0,-4)*{}="A";
    (18,-4)*{}="B";
    (18,4)*{}="B'";
    "B'";"1" **\crv{(18,10)& (12,10)};
    "A";"B" **\crv{(0,-14)&(18,-14)} ?(.04)*\dir{>};
    "B";"B'" **\dir{-} ?(.60)*\dir{>};
    (6,4)*{}="D1";
    (12,4)*{}="D2";
    (-6,-4)*{}="F1";
    (0,-4)*{}="F2";
    "D1";"D2" **\crv{(6,0)&(12,0)} ?(1)*\dir{<};
    "F1";"F2" **\crv{(-6,0)&(0,0)}
    ?(.03)*\dir{>};
    "3B";"F1" **\dir{-};
    \endxy


    \xy (-6,0)*{}="1E"; (6,0)*{}="3B";
    \endxy
    \qquad = \qquad \xy (-6,8)*{}="1E"; (-6,4)*{}="1"; (0,4)*{}="2";
    (6,4)*{}="3"; (-6,-8)*{}="3B";
    "2";"1" **\crv{(0,0)& (-6,0)}
    ?(.0)*\dir{>};
    "3";"2" **\crv{(6,10)& (-1,12)} ?(.05)*\dir{>};
    "1";"1E" **\dir{-}; ?(.25)*\dir{>};
    (12,4)*{}="1A";
    (0,-4)*{}="A";
    (18,-4)*{}="B";
    (18,4)*{}="B'";
    "B'";"1A" **\crv{(18,10)& (12,10)};
    "A";"B" **\crv{(0,-14)&(18,-14)} ?(.04)*\dir{>};
    "B";"B'" **\dir{-} ?(.60)*\dir{>};
    (6,4)*{}="D1";
    (12,4)*{}="D2";
    (-6,-4)*{}="F1";
    (0,-4)*{}="F2";
    "D1";"D2" **\crv{(6,0)&(12,0)} ?(1)*\dir{<};
    "F1";"F2" **\crv{(-6,0)&(0,0)}
    ?(.03)*\dir{>};
    "3B";"F1" **\dir{-};
    "1";"F1" **\dir{.};
    "2";"F2" **\dir{.};
    \endxy


    \xy (-6,0)*{}="1E"; (6,0)*{}="3B";
    \endxy
    \qquad = \qquad \xy (-6,8)*{}="1E"; (-6,4)*{}="1"; (0,4)*{}="2";
    (6,4)*{}="3"; (-6,-8)*{}="3B";
    "3";"2" **\crv{(6,10)& (-1,12)}
    ?(.05)*\dir{>} ?(1)*\dir{>};
    "1";"1E" **\dir{-};
    (12,4)*{}="1A";
    (0,-4)*{}="A";
    (18,-4)*{}="B";
    (18,4)*{}="B'";
    "B'";"1A" **\crv{(18,10)& (12,10)};
    "A";"B" **\crv{(0,-14)&(18,-14)};
    "B";"B'" **\dir{-} ?(.60)*\dir{>};
    (6,4)*{}="D1";
    (12,4)*{}="D2";
    (-6,-4)*{}="F1";
    (0,-4)*{}="F2";
    "D1";"D2" **\crv{(6,0)&(12,0)} ?(.95)*\dir{<};
    "3B";"F1" **\dir{-};
    "1";"F1" **\dir{-} ?(.47)*\dir{<};
    "2";"F2" **\dir{-};
    \endxy


    \xy (-6,0)*{}="1E"; (6,0)*{}="3B";
    \endxy
    \qquad = \qquad \xy (-6,8)*{}="1E"; (-6,4)*{}="1"; (0,4)*{}="2";
    (6,4)*{}="3"; (-6,-8)*{}="3B";
    "3";"2" **\crv{(6,10)& (-1,12)}
    ?(.05)*\dir{>} ?(1)*\dir{>};
    "1";"1E" **\dir{-};
    (12,4)*{}="1A";
    (0,-4)*{}="A";
    (18,-4)*{}="B";
    (18,4)*{}="B'";
    "B'";"1A" **\crv{(18,10)& (12,10)};
    "A";"B" **\crv{(0,-14)&(18,-14)};
    "B";"B'" **\dir{-} ?(.60)*\dir{>};
    (6,4)*{}="D1";
    (12,4)*{}="D2";
    (-6,-4)*{}="F1";
    (0,-4)*{}="F2";
    "D1";"D2" **\crv{(6,0)&(12,0)} ?(.95)*\dir{<};
    "3B";"F1" **\dir{-};
    "1";"F1" **\dir{-} ?(.47)*\dir{<};
    "2";"F2" **\dir{-};
    (-3,12)*{}="X1";
    (-3,0)*{}="X4";
    (15,12)*{}="X2";
    (15,0)*{}="X3";
    "X1";"X2" **\dir{.};
    "X2";"X3" **\dir{.};
    "X3";"X4" **\dir{.};
    "X4";"X1" **\dir{.};
    \endxy


    \xy (-6,0)*{}="1E"; (6,0)*{}="3B";
    \endxy
    \qquad = \qquad \xy (-6,8)*{}="1E"; (-6,-8)*{}="1"; (18,0)*{};
    "1";"1E" **\dir{-} ?(.53)*\dir{>};
    (6,4)*{}="1";
    (6,-4)*{}="A";
    (12,-4)*{}="B";
    (12,4)*{}="B'";
    "B'";"1" **\crv{(12,10)& (6,10)};
    "A";"B" **\crv{(6,-10)&(12,-10)};
    "B";"B'" **\dir{-} ?(.60)*\dir{>};
    "1";"A" **\dir{-}; ?(.57)*\dir{>};
    \endxy


    \xy (-6,0)*{}="1E"; (6,0)*{}="3B";
    \endxy
    \qquad = \qquad \xy (-6,8)*{}="1E"; (-6,-8)*{}="1"; (18,0)*{};
    "1";"1E" **\dir{-} ?(.53)*\dir{>};
    \endxy


    \xy
    (-6,-0)*{}="1";
    (0,0)*{}="2";
    (6,0)*{}="3";
    (6,-5)*{}="3'";
    (12,0)*{}="4";
    (12,-5)*{}="4'";
    "4";"1" **\crv{(12,18)& (-6,18)}
    ?(.03)*\dir{>} ?(1)*\dir{>};
    "1";"2" **\crv{(-6,-6)&(0,-6)};
    "2";"3" **\crv{(0,6)&(6,6)};
    ?(.04)*\dir{>} ;
    "3";"3'" **\dir{-}
    ?(.1)*\dir{>};
    "4";"4'" **\dir{-};
    \endxy


    \xy
    (-6,-0)*{}="1";
    (0,0)*{}="2";
    (0,-5)*{}="2'";
    (6,0)*{}="3";
    (-6,-5)*{}="0'";
    (6,0)*{}="A";
    (12,0)="B";
    "1";"0'" **\dir{-} ?(.05)*\dir{>};
    "B";"1" **\crv{(12,18)& (-6,18)};
    ?(.03)*\dir{>};
    "A";"B" **\crv{(6,-6)&(12,-6)}; ?(.02)*\dir{>};
    "2";"A" **\crv{(0,6) & (6,6)};
    ?(0.05)*\dir{>};
    "2'";"2" **\dir{-};
    \endxy


    \xy
    (-6,-0)*{}="1";
    (0,0)*{}="2";
    (6,0)*{}="3";
    (6,-5)*{}="3'";
    (12,0)*{}="4";
    (12,-5)*{}="4'";
    "4";"1" **\crv{(12,18)& (-6,18)}
    ?(.03)*\dir{>}
    ?(1)*\dir{>};
    "1";"2" **\crv{(-6,-6)&(0,-6)};
    "2";"3" **\crv{(0,6)&(6,6)};
    ?(.04)*\dir{>} ;
    "3";"3'" **\dir{-}
    ?(.1)*\dir{>};
    "4";"4'" **\dir{-};
    \endxy
    \qquad = \qquad
    \xy
    (-6,-0)*{}="1";
    (0,0)*{}="2";
    (0,-5)*{}="2'";
    (6,0)*{}="3";
    (-6,-5)*{}="0'";
    (6,0)*{}="A";
    (12,0)="B";
    "1";"0'" **\dir{-}
    ?(.05)*\dir{>};
    "B";"1" **\crv{(12,18)& (-6,18)};
    ?(.03)*\dir{>};
    "A";"B" **\crv{(6,-6)&(12,-6)};
    ?(.02)*\dir{>};
    "2";"A" **\crv{(0,6) & (6,6)};
    ?(0.05)*\dir{>};
    "2'";"2" **\dir{-};
    \endxy


    \xy
    (-6,-0)*{}="1";
    (0,0)*{}="2";
    (6,0)*{}="3";
    (12,0)*{}="4";
    (12,-8)*{}="4'";
    (6,-8)*{}="0";
    "4";"1" **\crv{(12,18)& (-6,18)};
    ?(.02)*\dir{>} ;
    "1";"2" **\crv{(-6,-6) & (0,-6)}
    ?(.04)*\dir{>};
    "2";"3" **\crv{(0,6) & (6,6)}; ?(0.02)*\dir{>} ;
    "4'";"4" **\dir{-};
    "3";"0" **\dir{-}
    ?(.1)*\dir{>} ;
    \endxy
    \qquad = \qquad \xy
    (-6,-0)*{}="1";
    (0,0)*{}="2";
    (6,0)*{}="3";
    (12,0)*{}="4";
    (12,-8)*{}="4'";
    (6,-8)*{}="0";
    "4";"1" **\crv{(12,18)& (-6,18)};
    "1";"2" **\crv{(-6,-6) & (0,-6)};
    ?(.04)*\dir{>};
    "2";"3" **\crv{(0,6) & (6,6)};
    ?(.02)*\dir{>} ;
    "4'";"4" **\dir{-};
    "3";"0" **\dir{-};
    (6,2)*{}="A";
    (6,-6)*{}="A'";
    (12,2)="B";
    (12,-6)="B'";
    "A";"B" **\crv{~*=<2pt>{.}(6,-2)&(12,-2)};
    "A'";"B'" **\crv{~*=<2pt>{.}(6,-2)&(12,-2)};
    \endxy


    \xy
    (12,0)*{};
    (-12,0)*{};
    \endxy
    \qquad = \qquad \xy
    (-6,-0)*{}="1";
    (0,0)*{}="2";
    (6,0)*{}="3";
    (12,0)*{}="4";
    (12,-10)*{}="4'";
    (6,-10)*{}="0'";
    (6,2)*{}="A";
    (6,-6)*{}="A'";
    (12,2)="B";
    (12,-6)="B'";
    "B";"1" **\crv{(12,18)& (-6,18)}
    ?(.03)*\dir{>};
    "1";"2" **\crv{(-6,-6) & (0,-6)}
    ?(.04)*\dir{>};
    "2";"A" **\crv{(0,6) & (6,6)};
    ?(.02)*\dir{>} ;
    "4'";"B'" **\dir{-};
    ?(.96)*\dir{>};
    "A'";"0'" **\dir{-}; ?(.5)*\dir{>};
    "A";"B" **\crv{(6,-2)&(12,-2)}; ?(0.05)*\dir{>} ;
    "B'";"A'" **\crv{(12,-2)&(6,-2)};
    \endxy


    \xy
    (12,0)*{};
    (-12,0)*{};
    \endxy
    \qquad = \qquad \xy
    (-6,-0)*{}="1";
    (0,0)*{}="2";
    (6,0)*{}="3";
    (12,0)*{}="4";
    (12,-10)*{}="4'";
    (6,-10)*{}="0'";
    (6,2)*{}="A";
    (6,-6)*{}="A'";
    (12,2)="B";
    (12,-6)="B'";
    "B";"1" **\crv{(12,18)& (-6,18)}
    ?(.03)*\dir{>};
    "1";"2" **\crv{(-6,-6) & (0,-6)}
    ?(.04)*\dir{>};
    "2";"A" **\crv{(0,6) & (6,6)};
    ?(.02)*\dir{>} ;
    "4'";"B'" **\dir{-}
    ?(.96)*\dir{>};
    "A'";"0'" **\dir{-} ?(.5)*\dir{>};
    "A";"B" **\crv{(6,-2)&(12,-2)}
    ?(.05)*\dir{>} ;
    "B'";"A'" **\crv{(12,-2)&(6,-2)};
    (-3,0)*{}="X";
    (9,-6)*{}="XX";
    "X";"XX" **\dir{--};
    \endxy


    \xy
    (12,0)*{};
    (-12,0)*{};
    \endxy
    \qquad = \qquad \xy
    (-6,2)*{}="1";
    (0,2)*{}="2";
    (6,0)*{}="3";
    (12,0)*{}="4";
    (0,-10)*{}="4'";
    (-6,-10)*{}="0'";
    (6,2)*{}="A";
    (-6,-6)*{}="A'";
    (12,2)="B";
    (0,-6)="B'";
    "B";"1" **\crv{(12,18)& (-6,18)}
    ?(.03)*\dir{>};
    "1";"2" **\crv{(-6,-2) & (0,-2)}
    ?(.04)*\dir{>};
    "2";"A" **\crv{(0,6) & (6,6)};
    ?(.05)*\dir{>} ;
    "4'";"B'" **\dir{-}
    ?(.96)*\dir{>};
    "A'";"0'" **\dir{-} ?(.5)*\dir{>};
    "A";"B" **\crv{(6,-2)&(12,-2)}
    ?(.05)*\dir{>} ;
    "B'";"A'" **\crv{(0,-2)&(-6,-2)};
    \endxy


    \xy
    (12,0)*{};
    (-12,0)*{};
    \endxy
    \qquad = \qquad \xy
    (-6,2)*{}="1";
    (0,2)*{}="2";
    (6,0)*{}="3";
    (12,0)*{}="4";
    (0,-10)*{}="4'";
    (-6,-10)*{}="0'";
    (6,2)*{}="A";
    (-6,-6)*{}="A'";
    (12,2)="B";
    (0,-6)="B'";
    "B";"1" **\crv{(12,18)& (-6,18)}
    ?(.03)*\dir{>};
    "1";"2" **\crv{(-6,-2) & (0,-2)}
    ?(.04)*\dir{>};
    "2";"A" **\crv{(0,6) & (6,6)};
    ?(.05)*\dir{>} ;
    "4'";"B'" **\dir{-}
    ?(.96)*\dir{>};
    "A'";"0'" **\dir{-} ?(.5)*\dir{>};
    "A";"B" **\crv{(6,-2)&(12,-2)}
    ?(.05)*\dir{>} ;
    "B'";"A'" **\crv{(0,-2)&(-6,-2)};
    "1";"A'" **\dir{.};
    "2";"B'" **\dir{.};
    \endxy


    \xy
    (-12,-0)*{};
    (12,0)*{};
    \endxy
    \qquad = \qquad \xy
    (-6,-0)*{}="1";
    (0,0)*{}="2";
    (0,-8)*{}="2'";
    (6,0)*{}="3";
    (-6,-8)*{}="0'";
    (6,2)*{}="A";
    (12,2)="B";
    "1";"0'" **\dir{-} ?(.05)*\dir{>};
    "B";"1" **\crv{(12,18)& (-6,18)};
    ?(.03)*\dir{>};
    "A";"B" **\crv{(6,-2)&(12,-2)};
    ?(.05)*\dir{>};
    "2";"A" **\crv{(0,6) & (6,6)};
    ?(.03)*\dir{>};
    "2'";"2" **\dir{-};
    \endxy


    \xy
    (0,-10)*++{}="g";
    (10,0)*{}="mid";
    **\crv{(5,20)} ?(.83)*\dir{>};
    (6.5,10)*{\scriptstyle i'_x};
    (20,10)*++{}="f";
    "f";"mid"; **\crv{(15,-20)} ?(0)*\dir{<} ?(.76)*\dir{<};
    (15.5,-10)*{\scriptstyle e'_x};
    \endxy
    \quad = \quad \xy (0,10)*{};(0,-10)*{}; **\dir{-}
    ?(.47)*\dir{<}+(3,1)
    \endxy


    \xy
    (0,10)*++{}="g";
    (10,0)*{}="mid";
    **\crv{(5,-20)} ?(.02)*\dir{>} ?(.83)*\dir{>};
    (6,-10)*{\scriptstyle e'_x};
    (20,-10)*++{}="f";
    "f";"mid"; **\crv{(15,20)} ?(.78)*\dir{<};
    (15,10)*{\scriptstyle i'_x};
    \endxy
    \quad = \quad \xy (0,10)*{};(0,-10)*{}; **\dir{-}
    ?(.53)*\dir{>}+(3,1)
    \endxy


    \vcenter{ \xy
    (-6,-0)*{}="1";
    (0,0) *{}="2";
    (6,0) *{}="3";
    (6,-5) *{}="3'";
    (12,0) *{}="4";
    (18,0) *={}="5";
    (18,12)*={}="5'";
    "5";"4" **\crv{(18,-6)& (12,-6)};
    "5'";"5" **\dir{-} ?(1)*\dir{>};
    "4";"1" **\crv{(12,18)& (-6,18)};
    ?(.03)*\dir{>} ?(1)*\dir{>};
    "1";"2" **\crv{(-6,-6)&(0,-6)};
    "2";"3" **\crv{(0,6)&(6,6)};
    ?(.08)*\dir{>} ;
    "3";"3'" **\dir{-}
    ?(0)*\dir{>};
    (16,-7)*{\scriptstyle e_{x}}; %\
    (4,7)*{\scriptstyle e_{x}^{-1}}; % LABELS FOR STRINGS
    (4,16)*{\scriptstyle i_{x}}; %/
    (-2,-7)*{\scriptstyle i_{x}^{-1}};
    \endxy}
    \qquad = \qquad \xy (0,8)*{};(0,-10)**\dir{-} ?(.53)*\dir{>};
    \endxy


    \vcenter{ \xy
    (-6,-0)*{}="1";
    (0,0)*{}="2";
    (6,0)*{}="3";
    (12,0)*{}="4";
    (12,-12)*{}="4'";
    (-12,12)*{}="0'";
    (-12,0)*{}="0";
    "4";"1" **\crv{(12,18)& (-6,18)};
    ?(.02)*\dir{>} ;
    "1";"2" **\crv{(-6,-6) & (0,-6)}
    ?(.04)*\dir{>};
    "2";"3" **\crv{(0,6) & (6,6)};
    ?(.08)*\dir{>} ;
    "4'";"4" **\dir{-};
    "3";"0" **\crv{(6,-18)&(-12,-18)}
    ?(.02)*\dir{>} ;
    "0";"0'" **\dir{-} ?(.05)*\dir{>};
    (3,16)*{\scriptstyle i_{x}};
    (-3,-16)*{\scriptstyle e_{x}};
    (-3,-7)*{\scriptstyle i_{x}^{-1}};
    (4,7)*{\scriptstyle e_{x}^{-1}};
    \endxy}
    \qquad = \qquad \xy (0,12)*{};(0,-12)**\dir{-} ?(.47)*\dir{<};
    \endxy


    \xy
    (-6,-0)*{}="1";
    (0,0) *{}="2";
    (6,0) *{}="3";
    (6,-5) *{}="3'";
    (12,0) *{}="4";
    (18,0) *={}="5";
    (18,12)*={}="5'";
    "5";"4" **\crv{(18,-6)& (12,-6)};
    "5'";"5" **\dir{-} ?(1)*\dir{>};
    "4";"1" **\crv{(12,18)& (-6,18)};
    ?(.03)*\dir{>} ?(1)*\dir{>};
    "1";"2" **\crv{(-6,-6)&(0,-6)};
    "2";"3" **\crv{(0,6)&(6,6)};
    ?(.08)*\dir{>} ;
    "3";"3'" **\dir{-}
    ?(0)*\dir{>};
    \endxy
    \qquad = \qquad \xy
    (-6,-0)*{}="1";
    (0,0)*{}="2";
    (6,0)*{}="3";
    (6,-5)*{}="3'";
    (12,0)*{}="4";
    (18,0)*={}="5";
    (18,12)*={}="5'";
    "5";"4" **\crv{(18,-6)& (12,-6)};
    "5'";"5" **\dir{-} ?(1)*\dir{>};
    "4";"1" **\crv{(12,18)& (-6,18)}
    ?(.03)*\dir{>} ?(1)*\dir{>};
    "1";"2" **\crv{(-6,-6)&(0,-6)};
    "2";"3" **\crv{(0,6)&(6,6)};
    ?(.08)*\dir{>} ;
    "3";"3'" **\dir{-}
    ?(0)*\dir{>} ;
    (3,0)*{}="A";
    (15,0)*{}="B";
    "A";"B" **\dir{--};
    \endxy


    \xy
    (-6,-0)*{}="1";
    (0,0) *{}="2";
    (6,0) *{}="3";
    (6,-5) *{}="3'";
    (12,0) *{}="4";
    (18,0) *={}="5";
    (18,12)*={}="5'";
    \endxy
    \qquad = \qquad \xy
    (-6,-0)*{}="1";
    (6,-5) *{}="2";
    (12,-5) *{}="3";
    (12,-10) *{}="3'";
    (6,5) *{}="4";
    (12,5) *={}="5";
    (12,10)*={}="5'";
    (18,0) *={}="";
    "5";"4" **\crv{(12,-1)& (6,-1)}
    ?(1)*\dir{>};
    "5'";"5" **\dir{-} ?(1)*\dir{>};
    "4";"1" **\crv{(4,12)& (-6,12)};
    ?(1)*\dir{>};
    "1";"2" **\crv{(-6,-12)&(4,-12)};
    "2";"3" **\crv{(6,1)&(12,1)};
    ?(.08)*\dir{>} ;
    "3";"3'" **\dir{-}
    ?(0)*\dir{>};
    \endxy


    \xy
    (-6,-0)*{}="";
    (18,0) *={}="";
    \endxy
    \qquad = \qquad \xy
    (-6,-0)*{}="1";
    (6,-5) *{}="2";
    (12,-5) *{}="3";
    (12,-10) *{}="3'";
    (6,5) *{}="4";
    (12,5) *={}="5";
    (12,10)*={}="5'";
    (18,0) *={}="";
    "5";"4" **\crv{(12,-1)& (6,-1)}
    ?(1)*\dir{>};
    "5'";"5" **\dir{-} ?(1)*\dir{>};
    "4";"1" **\crv{(4,12)& (-6,12)};
    ?(1)*\dir{>};
    "1";"2" **\crv{(-6,-12)&(4,-12)};
    "2";"3" **\crv{(6,1)&(12,1)};
    ?(.08)*\dir{>} ;
    "3";"3'" **\dir{-}
    ?(0)*\dir{>};
    "2";"4" **\dir{.};
    "3";"5" **\dir{.};
    \endxy


    \xy
    (-6,-0)*{}="";
    (18,0) *={}="";
    \endxy
    \qquad = \qquad \xy
    (6,0)*{}="1";
    (-6,0)*{}="2";
    "1";"2" **\crv{(7,15)&(-7,15)}
    ?(0)*\dir{>} ;
    "2";"1" **\crv{ (-7,-15)& (7,-15)}
    ?(.05)*\dir{>} ;
    \endxy
    \quad \xy (0,10)*{};(0,-10)**\dir{-} ?(.57)*\dir{>};
    \endxy \qquad


    \xy
    (-6,-0)*{}="1";
    (18,0) *={}="5";
    \endxy
    \qquad = \qquad \xy
    (6,0)*{}="";
    (-6,0)*{}="";
    \endxy
    \quad \xy (0,10)*{};(0,-10)**\dir{-} ?(.57)*\dir{>};
    \endxy \qquad


    \xy
    (-6,-0)*{}="1";
    (0,0)*{}="2";
    (6,0)*{}="3";
    (12,0)*{}="4";
    (12,-12)*{}="4'";
    (-12,12)*{}="0'";
    (-12,0)*{}="0";
    "4";"1" **\crv{(12,18)& (-6,18)};
    ?(.02)*\dir{>} ;
    "1";"2" **\crv{(-6,-6) & (0,-6)}
    ?(.04)*\dir{>};
    "2";"3" **\crv{(0,6) & (6,6)};
    ?(.08)*\dir{>} ;
    "4'";"4" **\dir{-};
    "3";"0" **\crv{(6,-18)&(-12,-18)}
    ?(.02)*\dir{>} ;
    "0";"0'" **\dir{-} ?(.05)*\dir{>};
    \endxy
    \qquad = \qquad \xy
    (-6,-0)*{}="1";
    (0,0)*{}="2";
    (0,-8)*{}="2'";
    (6,0)*{}="3";
    (-12,12)*{}="0'";
    (-12,0)*{}="0";
    (6,2)*{}="A";
    (12,2)="B";
    "0";"0'" **\dir{-} ?(.05)*\dir{>};
    "1";"0" **\crv{(-6,-12) &(-12,-12)}
    ?(.05)*\dir{>};
    "B";"1" **\crv{(12,18)& (-6,18)};
    ?(.03)*\dir{>};
    "A";"B" **\crv{(6,-2)&(12,-2)};
    ?(.08)*\dir{>};
    "2";"A" **\crv{(0,6) & (6,6)};
    ?(.03)*\dir{>};
    "2'";"2" **\dir{-};
    \endxy


    \xy
    (-12,-0)*{};
    (12,0)*{};
    \endxy
    \qquad = \qquad \xy
    (-6,-0)*{}="1";
    (0,0)*{}="2";
    (0,-8)*{}="2'";
    (6,0)*{}="3";
    (-12,12)*{}="0'";
    (-12,0)*{}="0";
    (6,2)*{}="A";
    (12,2)="B";
    "0";"0'" **\dir{-} ?(.05)*\dir{>};
    "1";"0" **\crv{(-6,-12) &(-12,-12)}
    ?(.05)*\dir{>};
    "B";"1" **\crv{(12,18)& (-6,18)};
    ?(.03)*\dir{>};
    "A";"B" **\crv{(6,-2)&(12,-2)};
    ?(.08)*\dir{>};
    "2";"A" **\crv{(0,6) & (6,6)};
    ?(.03)*\dir{>};
    "2'";"2" **\dir{-};
    (-9,-6)*{}="X";
    (3,1)*{}="XX";
    "X";"XX" **\dir{--};
    \endxy


    \xy
    (-12,-0)*{};
    (12,0)*{};
    \endxy
    \qquad = \qquad \xy
    (-12,12)*{}="0'";
    (-12,8)*{}="0";
    (-6,8)*{}="1";
    (-12,-2)*{}="2";
    (-12,-6)*{}="2'";
    (6,-2)*{}="3";
    (-6,-2)*{}="A";
    (0,-2)*{}="B";
    (0,8)*{}="B'";
    (12,0)*{}="";
    "0";"0'" **\dir{-} ?(.05)*\dir{>};
    "1";"0" **\crv{(-6,2) &(-12,2)}
    ?(.05)*\dir{>};
    "B'";"1" **\crv{(0,14)& (-6,14)};
    ?(.03)*\dir{>};
    "A";"B" **\crv{(-6,-6)&(0,-6)};
    ?(.04)*\dir{>};
    "2";"A" **\crv{(-12,4) & (-6,4)};
    ?(.03)*\dir{>};
    "2'";"2" **\dir{-};
    "B";"B'" **\dir{-} ?(.06)*\dir{>};;
    \endxy


    \xy
    (-12,-0)*{};
    (12,0)*{};
    \endxy
    \qquad = \qquad \xy
    (-12,12)*{}="0'";
    (-12,8)*{}="0";
    (-6,8)*{}="1";
    (-12,-2)*{}="2";
    (-12,-6)*{}="2'";
    (6,-2)*{}="3";
    (-6,-2)*{}="A";
    (0,-2)*{}="B";
    (0,8)*{}="B'";
    (12,0)*{}="";
    "0";"0'" **\dir{-} ?(.05)*\dir{>};
    "1";"0" **\crv{(-6,2) &(-12,2)}
    ?(.05)*\dir{>};
    "B'";"1" **\crv{(0,14)& (-6,14)};
    ?(.03)*\dir{>};
    "A";"B" **\crv{(-6,-6)&(0,-6)};
    ?(.04)*\dir{>};
    "2";"A" **\crv{(-12,4) & (-6,4)};
    ?(.03)*\dir{>};
    "2'";"2" **\dir{-};
    "B";"B'" **\dir{-} ?(.06)*\dir{>};
    "0";"2" **\dir{.};
    "1";"A" **\dir{.};
    \endxy


    \xy
    (-12,-0)*{};
    (12,0)*{};
    \endxy
    \qquad = \qquad \xy
    (-12,12)*{}="0'";
    (-6,8)*{}="1";
    (-12,-5)*{}="2'";
    (6,-2)*{}="3";
    (-6,-2)*{}="A";
    (0,-2)*{}="B";
    (0,8)*{}="B'";
    (12,0)*{}="";
    "B'";"1" **\crv{(0,14)& (-6,14)};
    "A";"B" **\crv{(-6,-6)&(0,-6)};
    "B";"B'" **\dir{-} ?(.60)*\dir{>};
    "2'";"0'" **\dir{-} ?(.53)*\dir{>};
    "1";"A" **\dir{-}; ?(.57)*\dir{>};
    \endxy


    \xy
    (-12,-0)*{};
    (12,0)*{};
    \endxy
    \qquad = \qquad \xy
    (-12,12)*{}="0'";
    (-12,-5)*{}="2'";
    (12,0)*{}="";
    "2'";"0'" **\dir{-} ?(.53)*\dir{>};
    \endxy


    \xy (-15,0)*{};(15,0)*{}; (-5,12)*{}; (-5,-12)*{};
    **\dir{-}?(.5)*\dir{<}+(-4,0)*{\scriptstyle F(x)};
    (5,0)*\xycircle(2.75,2.75){-}="f"; (5,12)**\dir{-}
    ?(.75)*\dir{>}+(5,-1)*{\scriptstyle \overline{F(x)}};
    "f";(5,-12)**\dir{-} ?(.5)*\dir{<}+(5,-1)*{\scriptstyle F(\xb)};
    (5,0)*{\scriptstyle F_{-1}};
    \endxy
    \qquad \qquad = \qquad \qquad \xy
    (6,15)*{};
    (-6,15)*{};
    **\crv{(0,-3)}
    ?(.22)*\dir{>}+(4,-5.5)*{\scriptstyle i_{F(x)}^{-1}}
    ?(.87)*\dir{>};
    (-6,-15)*{};
    (6,-15)*{};
    **\crv{(0,3)} ?(.20)*\dir{>} ?(.87)*\dir{>};+(-5,10.5)*{\scriptstyle \fix}
    \endxy


    \xy (0,0)*{\scriptstyle F_{-1}}; (-10,0)*{};(10,0)*{};
    (0,0)*\xycircle(2.75,2.75){-}="f"; (0,14)**\dir{-}
    ?(.75)*\dir{>}+(5,-1)*{\scriptstyle \overline{F(x)}};
    "f";(0,-14)**\dir{-} ?(.5)*\dir{<}+(5,-1)*{\scriptstyle F(\xb)};
    \endxy
    \qquad = \qquad \xy (-15,0)*{};(15,0)*{}; (-8,10)*{}="TL";
    (0,10)*{}="TR"; (-8,-10)*{}="BL"; (0,-10)*{}="BR";
    "TL";"BL" **\dir{-};
    ?(.5)*\dir{<};
    "TR";"BR" **\dir{-};
    ?(.5)*\dir{>};
    "TL";"TR" **\crv{(-8,18)& (0,18)};
    "BL";"BR" **\crv{(-8,-18)& (0,-18)};
    (8,0)*{\scriptstyle F_{-1}}; (8,0)*\xycircle(2.75,2.75){-}="f";
    (8,14)**\dir{-} ?(.75)*\dir{>}+(5,-1)*{\scriptstyle
    \overline{F(x)}}; "f";(8,-14)**\dir{-}
    ?(.5)*\dir{<}+(5,-1)*{\scriptstyle F(\xb)};
    (3.5,5)*{\scriptstyle F(x)};
    (-12,5)*{\scriptstyle \overline{F(x)}};
    \endxy


    \xy (-10,0)*{};(10,0)*{};
    \endxy
    \qquad = \qquad \xy (-15,0)*{};(15,0)*{}; (-8,10)*{}="TL";
    (0,10)*{}="TR"; (-8,-10)*{}="BL"; (0,-10)*{}="BR"; (8,10)*{}="RU";
    (8,-10)*{}="RB";
    "TL";"BL" **\dir{-};
    ?(.5)*\dir{<};
    "TR";"BR" **\dir{-};
    ?(.5)*\dir{>};
    "TL";"TR" **\crv{(-8,18)& (0,18)};
    "BL";"BR" **\crv{(-8,-18)& (0,-18)};
    "RU";"TR" **\crv{~*=<2pt>{.}(8,4)& (0,4)};
    "RB";"BR" **\crv{~*=<2pt>{.}(8,-4)& (0,-4)};
    (8,0)*{\scriptstyle F_{-1}}; (8,0)*\xycircle(2.75,2.75){-}="f";
    (8,14)**\dir{-} ?(.75)*\dir{>}+(5,-1)*{\scriptstyle
    \overline{F(x)}}; "f";(8,-14)**\dir{-}
    ?(.5)*\dir{<}+(5,-1)*{\scriptstyle F(\xb)};
    (-12,5)*{\scriptstyle \overline{F(x)}};
    \endxy


    \xy (-10,0)*{};(10,0)*{};
    \endxy
    \qquad = \qquad \xy (-15,0)*{};(15,0)*{}; (-8,10)*{}="TL";
    (0,10)*{}="TR"; (-8,-10)*{}="BL"; (0,-10)*{}="BR"; (8,10)*{}="RU";
    (8,16)*{}="RUEND"; (8,-16)*{}="RBEND"; (8,-10)*{}="RB";
    "TL";"BL" **\dir{-};
    ?(.5)*\dir{<};
    "RU";"RUEND" **\dir{-};
    ?(.15)*\dir{>}+(5,2)*{\scriptstyle \overline{F(x)}};
    "RB";"RBEND" **\dir{-};
    ?(0)*\dir{<}+(5,-2)*{\scriptstyle F(\xb)};
    "TL";"TR" **\crv{(-8,18)& (0,18)};
    ?(1)*\dir{>};
    "BL";"BR" **\crv{(-8,-18)& (0,-18)};
    ?(.95)*\dir{<}+(4,8)*{\scriptstyle \fix} ;;
    "RU";"TR" **\crv{(8,4)& (0,4)};
    "RB";"BR" **\crv{(8,-4)& (0,-4)};
    (-12,5)*{\scriptstyle \overline{F(x)}};
    \endxy


    \xy (-10,0)*{};(10,0)*{};
    \endxy
    \qquad = \qquad \xy (-15,0)*{};(15,0)*{}; (-8,10)*{}="TL";
    (0,10)*{}="TR"; (-8,-10)*{}="BL"; (0,-10)*{}="BR"; (8,10)*{}="RU";
    (8,16)*{}="RUEND"; (8,-16)*{}="RBEND"; (8,-10)*{}="RB";
    "TL";"BL" **\dir{-};
    ?(.5)*\dir{<};
    "RU";"RUEND" **\dir{-};
    ?(.15)*\dir{>}+(5,2)*{\scriptstyle \overline{F(x)}};
    "RB";"RBEND" **\dir{-};
    ?(0)*\dir{<}+(5,-2)*{\scriptstyle F(\xb)};
    "TL";"TR" **\crv{(-8,18)& (0,18)};
    ?(1)*\dir{>};
    "BL";"BR" **\crv{(-8,-18)& (0,-18)};
    ?(.95)*\dir{<}+(4,8)*{\scriptstyle \fix} ;;
    "RU";"TR" **\crv{(8,4)& (0,4)};
    "RB";"BR" **\crv{(8,-4)& (0,-4)};
    (16,20)*{}="X1";
    (-14,20)*{}="X2";
    (-14,3)*{}="X3";
    (16,3)*{}="X4";
    "X1";"X2" **\dir{.};
    "X2";"X3" **\dir{.};
    "X3";"X4" **\dir{.};
    "X4";"X1" **\dir{.};
    (-12,0)*{\scriptstyle \overline{F(x)}};
    \endxy


    \xy (-10,0)*{};(10,0)*{};
    \endxy
    \qquad = \qquad \xy (-15,0)*{};(15,0)*{}; (-8,10)*{}="TL";
    (-8,-10)*{}="BL"; (0,-10)*{}="BR"; (8,-16)*{}="RBEND";
    (8,-10)*{}="RB";
    "TL";"BL" **\dir{-};
    ?(.5)*\dir{<}+(5,8)*{\scriptstyle \overline{F(x)}};
    "RB";"RBEND" **\dir{-};
    ?(0)*\dir{<}+(5,-2)*{\scriptstyle F(\xb)};
    "BL";"BR" **\crv{(-8,-18)& (0,-18)};
    ?(.95)*\dir{<}+(4,8)*{\scriptstyle \fix} ;;
    "RB";"BR" **\crv{(8,-4)& (0,-4)};
    \endxy


    \xy (-15,0)*{};(15,0)*{}; (-5,12)*{}; (-5,-12)*{};
    **\dir{-}?(.5)*\dir{<}+(-4,0)*{\scriptstyle F(x)};
    (5,0)*{\scriptstyle F_{-1}}; (5,0)*\xycircle(2.75,2.75){-}="f";
    (5,12)**\dir{-} ?(.75)*\dir{>}+(5,-1)*{\scriptstyle
    \overline{F(x)}}; "f";(5,-12)**\dir{-}
    ?(.5)*\dir{<}+(5,-1)*{\scriptstyle F(\xb)};
    \endxy
    \qquad = \qquad \xy
    (-10,12)*{}; (-10,-12)*{}; **\dir{-}?(.5)*\dir{<}+(-4,0)*{\scriptstyle F(x)};
    (-2,12)*{}="1";
    (6,-7) *{}="2";
    (14,-7) *{}="3";
    (14,-13)*{}="3'";
    (18,0) *={}="";
    "1";"2" **\crv{(-4,-21)&(5,-15)};
    ?(.15)*\dir{<}+(5,10)*{\scriptstyle \overline{F(x)}};
    "2";"3" **\crv{(6,1)&(14,1)};
    ?(0)*\dir{<}+(4,8)*{\scriptstyle \fix} ;
    ?(.95)*\dir{<}+(5,-2)*{\scriptstyle F(\xb)};
    "3";"3'" **\dir{-}

    \endxy


    \xy (-15,0)*{};(15,0)*{};
    \endxy
    \qquad = \qquad \xy
    (-10,12)*{}; (-10,-12)*{}; **\dir{-}?(.5)*\dir{<}+(-4,0)*{\scriptstyle F(x)};
    (-2,12)*{}="1";
    (6,-7) *{}="2";
    (14,-7) *{}="3";
    (14,-13)*{}="3'";
    (18,0) *={}="";
    "1";"2" **\crv{(-4,-21)&(5,-15)};
    ?(.15)*\dir{<}+(5,10)*{\scriptstyle \overline{F(x)}};
    "2";"3" **\crv{(6,1)&(14,1)};
    ?(0)*\dir{<}+(4,8)*{\scriptstyle \fix} ;
    ?(.95)*\dir{<}+(5,-2)*{\scriptstyle F(\xb)};
    "3";"3'" **\dir{-};
    (-2,6)*{}="X1";
    (-10,6)*{}="X2";
    "X1";"X2" **\crv{~*=<2pt>{.}(-2,-1)&(-10,-1)};
    (-2,-6)*{}="XA";
    (-10,-6)*{}="XB";
    "XA";"XB" **\crv{~*=<2pt>{.}(-2,1)&(-10,1)};
    \endxy


    \xy (-15,0)*{};(15,0)*{};
    \endxy
    \qquad = \qquad \xy
    (-10,12)*{}="0";
    (-2,12)*{}="1";
    (6,-7) *{}="2";
    (14,-7) *{}="3";
    (14,-13)*{}="3'";
    (18,0) *={}="";
    (-2,6)*{}="X1";
    (-10,6)*{}="X2";
    (-2,-6)*{}="XA";
    (-10,-6)*{}="XB";
    (-10,-12)*{}="XB'";
    "XB";"XB'" **\dir{-}; ?(.4)*\dir{>};
    "X1";"1" **\dir{-}; ?(.3)*\dir{>};
    "X2";"0" **\dir{-}; ?(0)*\dir{<};
    "XA";"2" **\crv{(-1,-15)&(6,-15)};
    ?(0)*\dir{<};
    "2";"3" **\crv{(6,1)&(14,1)};
    ?(0)*\dir{<}+(4,8)*{\scriptstyle \fix} ;
    ?(.95)*\dir{<}+(5,-2)*{\scriptstyle F(\xb)};
    "3";"3'" **\dir{-};
    "X1";"X2" **\crv{(-2,-1)&(-10,-1)};
    "XA";"XB" **\crv{(-2,1)&(-10,1)};
    \endxy


    \xy (-15,0)*{};(15,0)*{};
    \endxy
    \qquad = \qquad \xy
    (-10,12)*{}="0";
    (-2,12)*{}="1";
    (6,-7) *{}="2";
    (14,-7) *{}="3";
    (14,-13)*{}="3'";
    (18,0) *={}="";
    (-2,6)*{}="X1";
    (-10,6)*{}="X2";
    (-2,-6)*{}="XA";
    (-10,-6)*{}="XB";
    (-10,-12)*{}="XB'";
    "XB";"XB'" **\dir{-}; ?(.4)*\dir{>};
    "X1";"1" **\dir{-}; ?(.3)*\dir{>};
    "X2";"0" **\dir{-}; ?(0)*\dir{<};
    "XA";"2" **\crv{(-1,-15)&(6,-15)};
    ?(0)*\dir{<};
    "2";"3" **\crv{(6,1)&(14,1)};
    ?(0)*\dir{<}+(4,8)*{\scriptstyle \fix} ;
    ?(.95)*\dir{<}+(5,-2)*{\scriptstyle F(\xb)};
    "3";"3'" **\dir{-};
    "X1";"X2" **\crv{(-2,-1)&(-10,-1)};
    "XA";"XB" **\crv{(-2,1)&(-10,1)};
    (-13,0)*{}="x1";
    (-13,-13)*{}="x2";
    (7,0)*{}="x4";
    (7,-13)*{}="x3";
    "x1";"x2"; **\dir{.};
    "x2";"x3"; **\dir{.};
    "x3";"x4"; **\dir{.};
    "x4";"x1"; **\dir{.};

    \endxy


    \xy (-15,0)*{};(15,0)*{};
    \endxy
    \qquad = \qquad \xy
    (-10,12)*{}="0";
    (-2,12)*{}="1";
    (6,-7) *{}="2";
    (6,-13) *{}="2'";
    (14,-7) *{}="3";
    (14,-13)*{}="3'";
    (18,0) *={}="";
    (-2,6)*{}="X1";
    (-10,6)*{}="X2";
    "X1";"1" **\dir{-}; ?(.3)*\dir{>};
    "X2";"0" **\dir{-}; ?(0)*\dir{<};
    "2";"3" **\crv{(6,1)&(14,1)};
    ?(0)*\dir{<}+(4,8)*{\scriptstyle \fix} ;
    ?(.95)*\dir{<}+(5,-2)*{\scriptstyle F(\xb)};
    "3";"3'" **\dir{-};
    "2";"2'" **\dir{-};
    "X1";"X2" **\crv{(-2,-1)&(-10,-1)};
    \endxy

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© 2004 Aaron Lauda
a.lauda@dpmms.cam.ac.uk