These are my questions:
(1) To prove that the diagram is commutative, we needs to prove that $gf=kh$, $wf=rv$, $zh=uv$, $sw=xg$, $xk=tz$, am I right?
(2) Suppose that the above diagram is commutative. Do the following equalities hold: $sr=tu$, $swf=xkh$
The multiplication above means composition of maps
Thanks in advance.