Xypic

Xypic is installed $\xymatrix{ %Our diagram is a 4x10 matrix &&&A_2\ar[rr]\ar[dd]|\hole^(.36){a_2}&&B_2\ar[rr]\ar[dd]|\hole^(.36){b_2}&&C_2\ar[rr]\ar[dd]|\hole^(.36){c_2}&&0\\ &&A_1\ar[rr]\ar[dd]^(.36){a_1}\ar[ur]&&B_1\ar[rr]\ar[dd]^(.36){b_1}\ar[ur]&&C_1\ar[rr]\ar[dd]^(.36){c_1}\ar[ur]&&0\\ &0\ar[rr]|(.475)\hole&&A'_2\ar[rr]|\hole&&B'_2\ar[rr]|\hole&&C'_2&&\\ 0\ar[rr]&&A'_1\ar[rr]\ar[ur]&&B'_1\ar[rr]\ar[ur]&&C'_1\ar[ur]&& }$

Not matrix example

$$\begin{xy} %vertices (27,0)*+{E^{[0]}=B}="v1";(0,20)*+{E^{[1]}}="v2";(70,20)*+{F^{[1]}}="v3";% (25,35)*+{K\left(\pi_1(F),1\right)}="v4";% (95,35)*+{K\left(\pi_1(F),1\right)}="v5";% (0,45)*+{\vdots}="v6";(70,45)*+{\vdots}="v7";(0,70)*+{E^{[n-1]}}="v8";% (70,70)*+{F^{[n-1]}}="v9";(25,85)*+{K\left(\pi_{n-1}(F),n-1\right)}="v10";% (95,85)*+{K\left(\pi_{n-1}(F),n-1\right)}="v11";(-20,100)*+{E}="v12";% (50,100)*+{F}="v13";(0,115)*+{E^{[n]}}="v14";(70,115)*+{F^{[n]}}="v15";% (25,130)*+{K\left(\pi_{n}(F),n\right)}="v16";% (95,130)*+{K\left(\pi_{n}(F),n\right)}="v17"; (0,150)*+{\vdots}="v18";(70,150)*+{\vdots}="v19"; {\ar@{->>}^{p_{n+1}} "v18"; "v14"};{\ar@{->>} "v19"; "v15"};% {\ar@{^{(}->} "v16";"v14" };{\ar@{^{(}->} "v17";"v15" };% {\ar@{_{(}->} "v15";"v14" };% {\ar@{->}^{h_{n}} "v12"; "v14"};{\ar@{->}^{h’_{n}} "v13"; "v15"};% {\ar@{_{(}->} "v13";"v12" }; {\ar@{->>}^{p_{n}}|(.33){\hole} "v14"; "v8"};% {\ar@{->}^{h_{n-1}} "v12"; "v8"};{\ar@{->}^{h_{1}} "v12"; "v2"};% {\ar@{->>} "v15"; "v9"};% {\ar@{->}^{h’_{n-1}} "v13"; "v9"};{\ar@{->}_{h’_{1}} "v13"; "v3"};% {\ar@{_{(}->} |(.18){\hole} "v9";"v8" };% {\ar@{^{(}->} "v10";"v8" };% {\ar@{^{(}->} "v11";"v9" }; {\ar@{->>} "v8"; "v6"};{\ar@{->>} "v9"; "v7"};% {\ar@{->>} "v6"; "v2"};{\ar@{->>} "v7"; "v3"};% {\ar@{^{(}->}|(.35){\hole} "v4";"v2" };% {\ar@{^{(}->} "v5";"v3" }; {\ar@{->}"v8"; "v1"};% {\ar@{_{(}->}|(.725){\hole} "v3";"v2" }; {\ar@{->>}_{q_1=p_1}"v2"; "v1"};% \end{xy}$$

Problems

This diagram doesn't display properly inside theorem boxes: FIXED

$$\begin{xy} \xymatrix{ R \ar[d] \ar[dr] &\\ A & B } \end{xy}$$

[Expand]

Theorem box

---

$$\begin{xy} \xymatrix{ R \ar[d] \ar[dr] &\\ A & B } \end{xy}$$

Samples

$$\newcommand{\bigudot}{ \mathchoice{\mathop{\bigcup\mkern-15mu\cdot\mkern8mu}}{\mathop{\bigcup\mkern-13mu\cdot\mkern5mu}}{\mathop{\bigcup\mkern-13mu\cdot\mkern5mu}}{\mathop{\bigcup\mkern-13mu\cdot\mkern5mu}} }$$ $$\newcommand{\udot}{\cup\mkern-12.5mu\cdot\mkern6.25mu\!}$$ $$\require{AMScd}\newcommand{\d}[1][]{\mathrm{d}^{#1} }$$

$$\begin{xy} \xymatrix { A \ar[r] \ar[d] \ar[drr] & B \ar[r] & *+{C} \ar@{}[] ="c" \\ D \ar[r] \ar[urr] & E \ar[r] & *+{F} \ar@{}[] ="f" \ar@2{->} "c";"f" } \end{xy}$$ $$\xymatrix{ A \ar[r] ^a ="a" & B \ar@2{->}[r] ^b="b" & C \ar @/^/ "a";"b" }$$

$$\begin{xy} %vertices (15,30)*+{\bigsqcup M_e}="v1";(45,30)*+{\bigsqcup N_e}="v2";% (0,15)*+{\bullet}="v3";(30,15)*+{\bullet}="v4";% (60,15)*+{\bullet}="v5";(15,0)*+{A}="v6";(45,0)*+{B}="v7";% %arrows {\ar@{->>} "v1"; "v3"}; {\ar@{->}_{m} "v1"; "v6"};% {\ar@{->>}^{p} "v1"; "v2"};{\ar@{->>} "v1"; "v4"};% {\ar@{->}_{n} "v2"; "v7"};{\ar@{->>} "v2"; "v5"};% {\ar@{>->}|{m’’} "v3";"v6"}; {\ar@{>->}|{(fm)’’} "v4"; "v7"};% {\ar@{->}|{n’’} "v5"; "v7"};{\ar@{->}_{f} "v6"; "v7"} \end{xy}$$

$$\begin{xy} \xymatrix { *\txt{start} \ar[r] & *++[o][F-]{0} \ar@(r,u)[]^b \ar[r]_a & *++[o][F-]{1} \ar[r]^b \ar@(r,d)[]_a & *++[o][F-]{2} \ar[r]^b \ar `dr_l[l] `_ur[l] _(.2)a[l] & *++[o][F=]{3} \ar `ur^l[lll] `^dr[lll]^b [lll] \ar `dr_l[ll] `_ur[ll] [ll] } \end{xy}$$