Section comma_proj_map_def.
Variable a b : Com_ob G x.
Definition Comma_proj_mor (f : a --> b) := Mor_com_arrow f.
Definition Comma_proj_map := Build_Map Comma_proj_map_law.
End comma_proj_map_def.

Lemma Comma_proj_comp_law : Fcomp_law Comma_proj_map.