diff --git a/test/gsc_test_ntree.erl b/test/gsc_test_ntree.erl
index 5e7f678..94cf9a9 100644
--- a/test/gsc_test_ntree.erl
+++ b/test/gsc_test_ntree.erl
@@ -70,6 +70,7 @@ f2f_op(OpStr, Fst) ->
 % never saw the op
 f2f_op(_opstr, Stk, []) ->
     lists:reverse(Stk);
+
 % see op
 f2f_op(OpStr, LhsStk, [#tk{str = OpStr} = OpTk | Rest]) ->
     Lhf = lists:reverse(LhsStk),
diff --git a/test/gsc_test_ytree.erl b/test/gsc_test_ytree.erl
new file mode 100644
index 0000000..6cbbe52
--- /dev/null
+++ b/test/gsc_test_ytree.erl
@@ -0,0 +1,27 @@
+-module(gsc_test_ytree).
+
+-include("$gsc_include/gsc.hrl").
+
+-export([main/0]).
+
+
+% @doc ys = syntax stem
+-record(ys,
+        {tks  :: [tk()],
+         sig  :: [tk()],
+         mta  :: any(),
+         fst  :: list(any())}).
+
+% syntax tree
+-type yt(StemT, LeafT) :: LeafT
+                        | #ys{mta :: StemT,
+                              fst :: [yt(StemT, LeafT)]}.
+
+% syntax forest
+-type yf(StemT, LeafT) :: [yt(StemT, LeafT)].
+
+
+main() ->
+    Src = "type foo = bar",
+    io:format("~ts~n", [Src]).
+