theorem Th95:
  A in con_class B iff A,B are_conjugated
proof
  thus A in con_class B implies A,B are_conjugated
  proof
    assume A in con_class B;
    then ex C st A = C & B,C are_conjugated;
    hence thesis;
  end;
  assume A,B are_conjugated;
  hence thesis;
end;
