Index: src/SynTree/TypeSubstitution.h
===================================================================
--- src/SynTree/TypeSubstitution.h	(revision 2ec65ad39e90408775929f92fdbbcf4a1b3bb9de)
+++ src/SynTree/TypeSubstitution.h	(revision d893266a116ebcf2881695a696009ec35c2807fe)
@@ -82,4 +82,11 @@
 	TypeEnvType typeEnv;
 	VarEnvType varEnv;
+
+  public:
+	// has to come after declaration of typeEnv
+	auto begin()       -> decltype( typeEnv.begin() ) { return typeEnv.begin(); }
+	auto   end()       -> decltype( typeEnv.  end() ) { return typeEnv.  end(); }
+	auto begin() const -> decltype( typeEnv.begin() ) { return typeEnv.begin(); }
+	auto   end() const -> decltype( typeEnv.  end() ) { return typeEnv.  end(); }
 };