Replace "iff" with "if and only if"

iff means if and only if, but readers without that knowledge might
assume this to be a spelling mistake. To me, this seems like
exclusionary language that is unnecessary. Simply using "if and only if"
instead should suffice.

1 files changed, 1 insertions, 1 deletions

diff --git a/thread.c b/thread.c
index 22b77b7f13..dce181d24e 100644
--- a/thread.c
+++ b/thread.c
@@ -5149,7 +5149,7 @@ recursive_list_access(VALUE sym)
 }
 
 /*
- * Returns Qtrue iff obj (or the pair <obj, paired_obj>) is already
+ * Returns Qtrue if and only if obj (or the pair <obj, paired_obj>) is already
  * in the recursion list.
  * Assumes the recursion list is valid.
  */