| ListP ps => let
            fun ifExists(x) = case ex of
            List xs => case (xs, ps) of
                (h::nil, g::nil) => match(h, g)
                | (h::t, g::r) => case match(h,g) of
                    SOME v => SOME (v @ (case match(List t, ListP r) of
                        SOME a => a
                        ))
                    | NONE => NONE
        in
            ifExists(ps)
        end