(* * This code was developped by IDEALX (http://IDEALX.org/) and * contributors (their names can be found in the CONTRIBUTORS file). It * is released under the terms of the BSD license (see LICENCE file * for details). *)
(****************************************************************** *                OPTION TYPE V0.1 (April 2001) * * ****************************************************************** * * The option type allows a function to have an error condition, a * way of making a partial function become total. * ******************************************************************)
Inductive option (A : Set) : Set :=
| none : option A
| some : A -> option A.

Lemma option_sum :
forall (A : Set) (o : option A), {y : A | o = some A y} + {o = none A}.