theorem Th25:
  |- f^<*p*> & |- f^<*'not' p*> implies |- f^<*q*>
proof
A1: Ant(f^<*p*>) = f & Suc(f^<*p*>) = p by CALCUL_1:5;
  assume |- f^<*p*> & |- f^<*'not' p*>;
  hence thesis by A1,CALCUL_1:44;
end;
