From a9b594f3991f67cf7d2c82a91d8c332c47c35ba7 Mon Sep 17 00:00:00 2001
From: Nathann Cohen <nathann.cohen@gmail.com>
Date: Fri, 15 Aug 2014 19:26:41 +0200
Subject: [PATCH] trac #16662: A comment about n<N-2

---
 src/sage/combinat/designs/orthogonal_arrays_recursive.py | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/sage/combinat/designs/orthogonal_arrays_recursive.py b/src/sage/combinat/designs/orthogonal_arrays_recursive.py
index de358bcf190..72c44afd62f 100644
--- a/src/sage/combinat/designs/orthogonal_arrays_recursive.py
+++ b/src/sage/combinat/designs/orthogonal_arrays_recursive.py
@@ -981,7 +981,8 @@ def find_thwart_lemma_3_5(k,N):
     k = int(k)
     N = int(N)
 
-    for n in prime_powers(k+2,N-2): # There must exist a OA(k+3,n)
+    for n in prime_powers(k+2,N-2): # There must exist a OA(k+3,n) thus n>=k+2
+                                    # At least 3 columns are nonempty thus n<N-2
 
         # we look for (m,n,a,b,c,d) with N = mn + a + b + c (+d) and
         # 0 <= a,b,c,d <= n