reserve x for set;
reserve a, b, c, d, e for Real;
reserve m, n, m1, m2 for Nat;
reserve k, l for Integer;
reserve p for Rational;

theorem Th61:
  2 to_power 3 = 8
proof
  thus 2 to_power 3 = 2 to_power (2+1) .= (2 to_power 2)*(2 to_power 1) by Th27
    .= 4*2 by Th60
    .= 8;
end;
