From 96f6680a404c579398e6e623d3f725ca084be699 Mon Sep 17 00:00:00 2001
From: Chung-chieh Shan <ccshan@iu.edu>
Date: Thu, 26 Feb 2026 00:50:04 -0500
Subject: [PATCH] =?UTF-8?q?Handle=20untyped=20=CE=BB=20in=20fvs?=
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---
 redex-lib/redex/tut-subst.rkt | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/redex-lib/redex/tut-subst.rkt b/redex-lib/redex/tut-subst.rkt
index 255c623c..5157eff2 100644
--- a/redex-lib/redex/tut-subst.rkt
+++ b/redex-lib/redex/tut-subst.rkt
@@ -97,6 +97,8 @@ for untyped.
     (match body
       [`(λ (,xs ,ts) ... ,body)
        (set-subtract (loop body) (apply set xs))]
+      [`(λ ,(? symbol? xs) ... ,body)
+       (set-subtract (loop body) (apply set xs))]
       [(? x?)
        (set body)]
       [(? list?)