theorem
  (M*(A\orB\orC))\iff(M*A)\or(M*B)\or(M*C) in H
  proof
A1: (M*(A\orB\orC))\iff(M*(A\orB))\or(M*C) in H by Def43;
    (M*(A\orB))\iff(M*A)\or(M*B) in H by Def43;
    hence thesis by A1,Th100;
  end;
