theorem Lem2A:
  x <=+=> y implies x <=*=> y
  proof
    assume
A1: x <=+=> y;
    consider z such that
A2: x <==> z & z <=*=> y by A1;
A3: x <=*=> z by A2,Th6;
    thus x <=*=> y by A2,A3,Th7;
  end;
