TRUE vs $$TRUE
Don't confuse TRUE with the pre-defined constant $$TRUE , which has the numeric value -1 .

  IF a THEN PRINT "a"

is not the same as

  IF (a = $$TRUE) THEN PRINT "a"

The first statement prints "a" as long as a is not zero. The second prints "a" only if a equals -1.

FALSE vs $$FALSE
Don't confuse FALSE with the pre-defined constant $$FALSE , which has a numeric value 0 .

  IFZ a$ THEN PRINT "a$ is empty"

is not the same as

  IF (a$ = $$FALSE) THEN PRINT "a$ is empty"

The second statement is a type mismatch since a$ is a string while $$FALSE is a number.