replaced apply-style proof for instance Multiset :: plus_ac0 by recommended Isar proof style
(*** Addition with fixpoint of successor ***)Ex3 = LCF +consts s :: "'a => 'a" p :: "'a => 'a => 'a"rules p_strict "p(UU) = UU" p_s "p(s(x),y) = s(p(x,y))"end