val pair : ?eq:( ('a * 'b) -> ('a * 'b) -> bool ) -> 'a signal -> 'b signal -> ('a * 'b) signal
val fst : ?eq:( 'a -> 'a -> bool ) -> ('a * 'b) signal -> 'a signal
val snd : ?eq:( 'a -> 'a -> bool ) -> ('b * 'a) signal -> 'a signal