theorem
  for H1,H2 being strict Subgroup of G holds H1 in con_class H2 implies
  H2 in con_class H1
proof
  let H1,H2 be strict Subgroup of G;
  assume H1 in con_class H2;
  then H1,H2 are_conjugated by Th107;
  hence thesis by Th107;
end;
