X-Git-Url: http://matita.cs.unibo.it/gitweb/?a=blobdiff_plain;f=matita%2Flibrary%2Fdatatypes%2Fconstructors.ma;h=6d0a68503bb809a72c689be947ef81f38e812c89;hb=562e9adf40098e11d8f0bc2711a7f665360c2231;hp=3567dd915463c8b6c2f809ed8218987a67e78042;hpb=0ed7fb39e919a6a4814dc5e9d435edf924cca72f;p=helm.git

diff --git a/matita/library/datatypes/constructors.ma b/matita/library/datatypes/constructors.ma
index 3567dd915..6d0a68503 100644
--- a/matita/library/datatypes/constructors.ma
+++ b/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