[NTG-context] Nodes module for commutative diagrams etc

Dear list, I need to typeset a handful of simple commutative diagrams like the one below, and I found the nodes manual by Alan that has exactly what I want. But what is the incantation to load the module, or am I missing something else? Thanks, Matthias \starttext \startMPcode path p ; p := fullsquare scaled 3cm ; nodepath = p ; draw node(0,"\node{$G(X)$}") ; draw node(1,"\node{$G(Y)$}") ; draw node(2,"\node{$F(Y)$}") ; draw node(3,"\node{$F(X)$}") ; drawarrow fromto.bot(0,0,1, "\nodeSmall{$G(f)$}") ; drawarrow fromto.top(0,3,2, "\nodeSmall{$F(f)$}") ; drawarrow fromto.rt (0,2,1, "\nodeSmall{$η_Y$}") ; drawarrow fromto.lft(0,3,0, "\nodeSmall{$η_X$}") ; \stopMPcode \stoptext