From a3757ddbd7cdad4e36fd73985c9d7f57dc11667a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?V=C3=ADtor=20Santos=20Costa?= <vsc@dcc.fc.up.pt>
Date: Tue, 2 Oct 2012 15:16:30 +0100
Subject: [PATCH] more examples.

---
 library/coinduction.yap | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/library/coinduction.yap b/library/coinduction.yap
index 4b259417d..ecbb5e038 100644
--- a/library/coinduction.yap
+++ b/library/coinduction.yap
@@ -166,5 +166,31 @@ stream([H|T]) :- i(H), stream(T).
 i(0).
 i(s(N)) :- i(N).
 
+	% Are there infinitely many "occurrences" of arg1 in arg2?
+	:- coinductive comember/2.
+
+	comember(X, L) :-
+		drop(X, L, L1),
+		comember(X, L1).
+
+	% Drop some prefix of arg2 upto an "occurrence" of arg1 from arg2,
+	% yielding arg3.
+	% ("Occurrence" of X = something unifiable with X.)
+	%:- table(drop/3).	% not working; needs tabling supporting cyclic terms!
+	drop(H, [H| T], T).
+	drop(H, [_| T], T1) :-
+		drop(H, T, T1).
+
+
+% X = [1, 2, 3| X], comember(E, X).
+
+        user:p(E) :- 
+                X = [1, 2, 3| X],
+                comember(E, X),
+                format('~w~n',[E]), 
+                get_code(_),
+                fail.
+
+
 **************************************/