fact: Definition ab_kernel {A B : AbGroup} (f : A $-> B) : AbGroup := Build_AbGroup (grp_kernel f) _.
imports: Basics Types Classes.interfaces.canonical_names (Zero, zero) Classes.interfaces.abstract_algebra (IsAbGroup(..), abgroup_group, abgroup_commutative) Algebra.Groups.Group Algebra.Groups.Subgroup Algebra.Groups.QuotientGroup WildCat