The phrase `IS FALSE` means `== 0` while the phrase `IS TRUE` means `<> 0`. The constant `FALSE` means 0, and the constant `TRUE` means `1`. `x IS TRUE` means `x <> 0` -- `IS TRUE` means `<> 0` `TRUE IS x` means `1 IS x` -- `TRUE IS` means `1 ==` (True is a constant in this case, not a test). IS and TRUE are not commutative. `IS TRUE` is not the same as `TRUE IS` IS and FALSE are commutative. `IS FALSE` is the same as `FALSE IS`