type number =
    [ `NCst of num			(** numeric constant *)
    | `Ninf				(** positive infinity *)
    | `Neginf				(** negative infinity *)
    ]

type variable =
    [ `EVar of string			(** (existential) variable *)
    | `UVar of string			(** constant (universal
					    variable) *)
    ]

type num_coef =
    [ `Mult of num * variable		(** constant coefficient *)
    ]

type numeric =
    [ number | num_coef
    | `Add of num_coef list * number	(** linear combination *)
    ]
;;

type construct =
    [ `TCons of string * typ list
    | `Fun of proper_typ * proper_typ
    ]

and proper_typ = [variable | construct]

and typ = [proper_typ | numeric]
;;