[Pietrovich]

совсем конкретно по вопросу:

trace(undefined >= 0);

//==================
movie 'Untitled-1.swf' // flash 6, total frames: 1, frame rate: 12 fps, 550x400 px

frame 0
push UNDEF, 0.0
lessThan
not
trace
end // of frame 0
end