Hemos habilitado el \usepackage[all]{xy}, que permite hacer diagramas en TeX. Del siguiente enlace obtuvimos los ejemplos que se muestran, donde hay una explicación sobre cómo utilizar las instrucciones.
http://www.uv.es/~ivorra/Latex/XY.pdf#search=%22usepackage%20xy%22 
[tex]\xymatrix{ A & B & C \\ D \ar[rru] & E }[/tex]
[tex]
\xymatrix{A\ar@(ul,dl)[l]\ar@(ur,r)[r] &B}[/tex]
Otro link:
http://zoonek2.free.fr/UNIX/11_xypic/index.html
[tex]\xymatrix{
A \ar[r] \ar[d] \ar[rd] & B \ar[d] \\
C \ar[r] & D
}[/tex]
[tex] \xymatrix{A \ar[r]^f \ar[d]_\phi \ar[rd] & B \ar[d]^\psi \\ C \ar[r]_g & D }[/tex]
[tex] \xymatrix @!0 @R=2pc @C=3pc { A \ar[rr] \ar[rd] \ar[dd] && B \ar[dd] \\ & C \ar[ru] \ar[dd] \\A' \ar[rr] |!{[ur];[dr]}\hole \ar[rd] && B' \\& C' \ar[ru] }[/tex]
[tex] \xymatrix {
A \ar[rr] \ar[dd] \ar[dr] && B \ar[dr] \ar[dd] |!{[dl];[dr]}\hole \\
& A \ar[rr] \ar[dd] && B' \ar[dd] \\
C \ar[rr] |!{[ur];[dr]}\hole \ar[dr] && D \ar[rd] \\
& C' \ar[rr] && D' \\
}[/tex]
Colaboración de
arcmath[center][tex]\xy 0;/r2.2pc/:(0.1,0)*{};(4,0)*{};**\dir{.};(-0.1,0)*{};(-4,0)*{};**\dir{.};(0,1.8)*{};(0,3.3)*{};**\dir{.};
(0,1.8)*{};(0,0.01)*{};**\dir{.};(0,-0.7)*{};(0,0)*{};**\dir{.};{(-3,0)*{};(3,0)*{};**\crv{(2,3.7)&(-2,3.7)}};
{(-1,0)*{};(1,0)*{};**\crv{(0.7,1)&(-0.7,1)}};(1,0)*{};(3,0)*{};**\dir{-};(-3,0)*{};(-1,0)*{};**\dir{-};(0,0)*{\circ};
(3,0)*{\bullet};(-3,0)*{\bullet};(1,0)*{\bullet};(-1,0)*{\bullet};(-0.2,-0.2)*{0};
(-1.2,-0.3)*{-r};(1,-0.3)*{r};(-3.2,-0.3)*{-R};(3,-0.3)*{R};(2.8,2.8)*{\gamma};(-2.6,2)*{C_R};(1,0.7)*{C_r};(-2,0)*{>};
(-3.7,0.2)*{x};(-0.2,3.3)*{y};
(2,0)*{>};(0,0.75)*{>};(0,2.77)*{<};\endxy[/tex][/center]
