reserve S for non empty non void ManySortedSign,
  A for MSAlgebra over S;
reserve A for non-empty MSAlgebra over S;
reserve S for non empty non void ManySortedSign,
  A for non-empty MSAlgebra over S,
  R for ManySortedRelation of the Sorts of A;

theorem
  StabCl R c= TRS R & InvCl R c= TRS R & StabCl InvCl R c= TRS R
proof
  R c= TRS R by Def13;
  hence StabCl R c= TRS R & InvCl R c= TRS R by Def11,Def12;
  hence thesis by Def12;
end;
