refactor(library/algebra/category/morphism): restore previous (and more readable) proofs
refactor(library/algebra/category/morphism): restore previous (and more readable) proofs

fpvandoorn/lean2,fpvandoorn/lean,UlrikBuchholtz/lean,c-cube/lean,fpvandoorn/lean2,dselsam/lean,fgdorais/lean,soonhokong/lean-windows,sp3ctum/lean,dselsam/lean,javra/lean,UlrikBuchholtz/lean,avigad/lean,leodemoura/lean,dselsam/lean,Kha/lean,johoelzl/lean,eigengrau/lean,dselsam/lean,soonhokong/lean-windows,levnach/lean,Kha/lean,digama0/lean,levnach/lean,eigengrau/lean,c-cube/lean,fpvandoorn/lean,soonhokong/lean-windows,soonhokong/lean-osx,leanprover-community/lean,leanprover-community/lean,soonhokong/lean-osx,fpvandoorn/lean2,levnach/lean,johoelzl/lean,soonhokong/lean,levnach/lean,leanprover/lean,sp3ctum/lean,leanprover/lean,dselsam/lean,digama0/lean,c-cube/lean,Kha/lean,c-cube/lean,eigengrau/lean,johoelzl/lean,leanprover-community/lean,dselsam/lean,johoelzl/lean,c-cube/lean,htzh/lean,leodemoura/lean,Kha/lean,digama0/lean,fgdorais/lean,javra/lean,htzh/lean,leanprover/lean,rlewis1988/lean,javra/lean,rlewis1988/lean,UlrikBuchholtz/lean,johoelzl/lean,soonhokong/lean-osx,avigad/lean,sp3ctum/lean,Kha/lean,Kha/lean,soonhokong/lean,fpvandoorn/lean,levnach/lean,fpvandoorn/lean,rlewis1988/lean,fpvandoorn/lean2,johoelzl/lean,eigengrau/lean,javra/lean,fgdorais/lean,UlrikBuchholtz/lean,leanprover-community/lean,javra/lean,sp3ctum/lean,leanprover-community/lean,fpvandoorn/lean2,rlewis1988/lean,fpvandoorn/lean,htzh/lean,digama0/lean,soonhokong/lean,eigengrau/lean,htzh/lean,soonhokong/lean-windows,sp3ctum/lean,fgdorais/lean,digama0/lean,leodemoura/lean,leanprover/lean,htzh/lean,avigad/lean,leanprover/lean,soonhokong/lean-osx,fpvandoorn/lean,fgdorais/lean,avigad/lean,avigad/lean,digama0/lean,soonhokong/lean,leodemoura/lean,UlrikBuchholtz/lean,rlewis1988/lean,leodemoura/lean,leanprover-community/lean,leanprover/lean,fgdorais/lean,soonhokong/lean-windows,leodemoura/lean,avigad/lean,soonhokong/lean-osx,rlewis1988/lean,soonhokong/lean