SIGNATURE OptionCompare[data]

-- comparing options

-- Parameter
SORT data

IMPORT Option[data] ONLY option
       RelCmp       ONLY rel < = >

FUN cmp  : (data ** data -> bool) -> option[data] ** option[data] -> rel
           -- cmp (<) (s1, s2)
           -- lifting of < to options
           -- given a total, irreflexive order, produces
           -- such an order. 

FUN eq?  : (data ** data -> bool) -> option[data] ** option[data] -> bool
           -- equality
           -- (should be used with an equivalence relation)