SIGNATURE SetOfSet[data, < :data ** data -> bool]

-- functions using sets of sets

IMPORT  Set[data, <] ONLY set[data,<] {<}[data,<]
        Set[set[data, <], {<}] ONLY set[set[data, <], {<}'Set[data,<]]

-- Parameter
SORT data
FUN <   : data ** data -> bool
        -- total strict-order; in 
        --   ~(x < y) AND ~(y < x) => x = y
        -- should = represent semantic equality

FUN flat : set[set[data, <], {<}] -> set[data, <]
           -- flatten sets

FUN P : set[data, <] -> set[set[data, <], {<}]
        -- power set

FUN partition: (data ** data -> bool) -> set[data, <] -> set[set[data, <], {<}]
        -- partition set according to equivalence relation