reserve n for non zero Nat,
  j,k,l,m for Nat,
  g,h,i for Integer;

theorem Th15:
  for z be Tuple of 1,BOOLEAN st z=<*TRUE*> holds Intval(z) = -1
proof
  let z be Tuple of 1,BOOLEAN such that
A1: z = <*TRUE*>;
  len z = 1 by CARD_1:def 7;
  then z/.1 = z.1 by FINSEQ_4:15
    .= TRUE by A1;
  then Intval(z) = Absval(z) - 2 to_power 1 by BINARI_2:def 3
    .= 1 - 2 to_power 1 by A1,BINARITH:16
    .= 1 - (1 + 1) by POWER:25
    .= 0 - 1;
  hence thesis;
end;
