reserve x, y for set;
reserve D for non empty set;
reserve UN for Universe;
reserve C for Category;
reserve O for non empty Subset of the carrier of C;
reserve G,H for AddGroup;
reserve V for Group_DOMAIN;

theorem Th24:
  for f being strict GroupMorphism holds {f} is GroupMorphism_DOMAIN
proof
  let f be strict GroupMorphism;
  for x being object st x in {f} holds x is strict GroupMorphism
   by TARSKI:def 1;
  hence thesis by Def16;
end;
