some improvements

[helm.git] / helm / software / matita / library / datatypes / constructors.ma

diff --git a/helm/software/matita/library/datatypes/constructors.ma b/helm/software/matita/library/datatypes/constructors.ma
index 3567dd915463c8b6c2f809ed8218987a67e78042..6d0a68503bb809a72c689be947ef81f38e812c89 100644 (file)
--- a/helm/software/matita/library/datatypes/constructors.ma
+++ b/helm/software/matita/library/datatypes/constructors.ma
@@ -17,7 +17,9 @@ include "logic/equality.ma".
 
 inductive void : Set \def.
 
-inductive Prod (A,B:Set) : Set \def
+inductive unit : Set ≝ something: unit.
+
+inductive Prod (A,B:Type) : Type \def
 pair : A \to B \to Prod A B.
 
 interpretation "Pair construction" 'pair x y =
@@ -70,4 +72,8 @@ match p with
 
 definition sndT \def \lambda A,B:Type.\lambda p: ProdT A B.
 match p with
-[(pairT a b) \Rightarrow b].
\ No newline at end of file
+[(pairT a b) \Rightarrow b].
+
+inductive option (A:Type) : Type ≝
+   None : option A
+ | Some : A → option A.
\ No newline at end of file