val list_nth: int -> ('a * 'b) list -> 'b
val list_toggle: int -> (bool * 'b) list -> (bool * 'b) list
val list_toggle_all: (bool * 'b) list -> (bool * 'b) list
val list_nth: int -> ('a * 'b) list -> 'b
val list_toggle: int -> (bool * 'b) list -> (bool * 'b) list
val list_toggle_all: (bool * 'b) list -> (bool * 'b) list