list partition

[Moosebumps]

Is there a function that takes a list and predicate, and returns two
lists -- one for which the predicate is true and one for which it is false?

I know I can call filter(p, list) and filter( not p, list) or something like
that, but I assume it would be more efficient to do it in one pass.

Actually I probably can't call "not p", I would have to wrap p in a function
notP or something.  Or is there a shortcut for lambda(x) : not p(x)?  I
guess it isn't that long : )

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