Cat1MorphismOps.CompositeMorphism( mu1,mu2 )
Morphisms mu_1 : C to D and mu_2 : D to E have a composite mu = mu_2 circ mu_1 : C to E whose source and range homomorphisms are the composites of those of mu_1 and mu_2. The example corresponds to that in refCompositeMorphism for crossed modules.
gap> psi;
Morphism of crossed modules <[c4->q8] >-> [c4->q8]>
gap> inc;
Morphism of crossed modules <[c4->q8] >-> [q8->sl(2,3)]>
gap> mupsi := Cat1MorphismXModMorphism( psi );
Morphism of cat1-groups
<[Perm(q8 |X c4) ==> q8]-->[Perm(q8 |X c4) ==> q8]>
gap> muinc := Cat1MorphismXModMorphism( inc );
Morphism of cat1-groups
<[Perm(q8 |X c4) ==> q8]-->[Perm(sl(2,3) |X q8) ==> sl(2,3)]>
gap> mucomp := Cat1MorphismOps.CompositeMorphism( mupsi, muinc );
Morphism of cat1-groups
<[Perm(q8 |X c4) ==> q8]-->[Perm(sl(2,3) |X q8) ==> sl(2,3)]>
gap> muxcomp := Cat1MorphismXModMorphism( xcomp );;
gap> mucomp = muxcomp;
true
GAP 3.4.4