Not

{00} Not

Not()

Variable 0 = (Variable 0 <= 0)

Or in other words, a TRUE becomes a FALSE, and a FALSE becomes a TRUE.

See also: {01} If

Note: If placed inside an If block, may yank passing command runs into the If block at that point in time even when they should be skipping over it. Tested by putting a SoundEffect/Pause combo immediately before and after the Not command when it shouldn't have been being run; only the one after the Not command was processed, followed by the rest of the commands after it. May have required some other factors, but still.