filter : ('a -> bool) -> 'a list -> 'a list
STRUCTURE
SYNOPSIS
Filters a list to the sublist of elements satisfying a predicate.
DESCRIPTION
filter P l applies P to every element of l, returning a list of those that satisfy P, in the order they appeared in the original list.
FAILURE
If P x fails for some element x of l.
COMMENTS
Identical to List.filter from the Standard ML Basis Library.
SEEALSO
HOL  Kananaskis-14