SIGNATURE BitsetFilter

--

IMPORT Bitset ONLY set
       Nat ONLY nat

FUN |        : (nat -> bool) ** set -> set              
                -- p | s 
                -- filter: select all elements of s fulfilling predicate p

FUN partition: (nat -> bool) ** set -> set ** set       
                -- partition (p, s) == (s1,s2)
                -- s1, s2 are subsets of s; s1 + s2 = s
                -- predicate p evaluating true for elements of s1
                -- predicate p evaluating false for elements of s2