feat(library/locals): add auxiliary method
feat(library/locals): add auxiliary method

leanprover/lean,soonhokong/lean-osx,rlewis1988/lean,dselsam/lean,leanprover-community/lean,leodemoura/lean,rlewis1988/lean,digama0/lean,avigad/lean,dselsam/lean,johoelzl/lean,fpvandoorn/lean,fpvandoorn/lean,leodemoura/lean,digama0/lean,leanprover-community/lean,avigad/lean,digama0/lean,leodemoura/lean,dselsam/lean,fgdorais/lean,Kha/lean,soonhokong/lean-osx,avigad/lean,soonhokong/lean-osx,fpvandoorn/lean,fgdorais/lean,Kha/lean,leanprover/lean,digama0/lean,leanprover-community/lean,leanprover/lean,fgdorais/lean,rlewis1988/lean,leanprover-community/lean,fgdorais/lean,digama0/lean,johoelzl/lean,soonhokong/lean-windows,leanprover/lean,leodemoura/lean,soonhokong/lean-windows,fpvandoorn/lean,rlewis1988/lean,leanprover/lean,rlewis1988/lean,avigad/lean,leodemoura/lean,leanprover-community/lean,dselsam/lean,dselsam/lean,dselsam/lean,Kha/lean,johoelzl/lean,leanprover-community/lean,johoelzl/lean,Kha/lean,johoelzl/lean,fpvandoorn/lean,soonhokong/lean-windows,soonhokong/lean-windows,soonhokong/lean-osx,fgdorais/lean,Kha/lean,avigad/lean,soonhokong/lean-windows,soonhokong/lean-osx,johoelzl/lean,fpvandoorn/lean,fgdorais/lean,digama0/lean,Kha/lean,avigad/lean,leanprover/lean,leodemoura/lean,rlewis1988/lean