refactor(library/unifier): use new assign method in the unifier
refactor(library/unifier): use new assign method in the unifier

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