is mentioned by

Thm* f:(AB). f o Id = f	[comp_id_r]
Thm* f:(AB). Id o f = f	[comp_id_l]
Def InvFuns(A; B; f; g) == g o f = Id & f o g = Id	[inv_funs]

Try larger context: StandardLIB IF YOU CAN SEE THIS go to /sfa/Nuprl/Shared/Xindentation_hack_doc.html