User:Alec/Bitchin

[math]\xymatrix{ & C_n(X) \ar@{-->}[drr]^{\pi_3\circ f} \ar[rr]^f \ar[d]_{\pi_1} \ar[dl]_{\pi_2} & & C_{n-1}(X) \ar[d]^{\pi_3} & \\ \frac{C_n(X)}{\text{Ker}(f)} \ar@{-->}@/_4.5ex/[rrr]_{\pi_3\circ f_2'}\ar@{.>}@/^9.5ex/[urrr]^{f_2'} & \frac{C_n(X)}{C_n(A)} & & \frac{C_{n-1}(X)}{C_{n-1}(A)} & }[/math]
Here it is