
theorem Th5:
  for A1,A2 being AdjectiveStr st the AdjectiveStr of A1 = the
  AdjectiveStr of A2 holds A1 is involutive implies A2 is involutive
proof
  let A1,A2 be AdjectiveStr such that
A1: the AdjectiveStr of A1 = the AdjectiveStr of A2;
  assume
A2: for a being adjective of A1 holds non-non-a = a;
  let a be adjective of A2;
  reconsider b = a as adjective of A1 by A1;
  thus non-non-a = non-non-b by A1
    .= a by A2;
end;
