diff --git a/src/expresses.ts b/src/expresses.ts
index f439dc3..8f2d4dd 100644
--- a/src/expresses.ts
+++ b/src/expresses.ts
@@ -13,6 +13,10 @@ class TraitExpression<
         readonly traits:      Traits,
     ) {}
 
+    then<V>(fn: (e: this) => V): V {
+        return fn(this)
+    }
+
     extends(): (
         AbstractClass<
             Pipe<[
@@ -91,6 +95,7 @@ type ExtendsAndExpressesReturnType<
     Super  extends AbstractClass<any>,
     Traits extends readonly Trait<any, any>[],
 > = (
+    Call<Tuples.IsEmpty, Traits>               extends false ?
     AbstractMembersExtendable<Super, Traits>   extends true ?
     ImplInstanceExtendable<Super, Traits>      extends true ?
     ImplStaticMembersExtendable<Super, Traits> extends true ?
@@ -98,6 +103,7 @@ type ExtendsAndExpressesReturnType<
     : "Type conflict between the traits implementation static members and/or the superclass static members."
     : "Type conflict between the traits implementation instances and/or the superclass instance."
     : "Type conflict between the traits abstract members and/or the superclass instance."
+    : "Cannot express an empty list of traits."
 )
 
 export function extendsAndExpresses<
diff --git a/src/tests.ts b/src/tests.ts
index 2555515..b94dbe6 100644
--- a/src/tests.ts
+++ b/src/tests.ts
@@ -48,15 +48,16 @@ class TestSuperclass {
 }
 
 
-const exp = extendsAndExpresses(
+const User = extendsAndExpresses(
     TestSuperclass,
     Identifiable<bigint>(),
     // Identifiable<number>()
+).then(e =>
+    class User
+    extends e.extends()
+    implements Implements<typeof e> {
+        id: bigint = -1n
+    }
 )
-// type ExpImpl = ImplStaticMembersExtendable<typeof TestSuperclass, typeof exp.traits>
-
-class User extends exp.extends() implements Implements<typeof exp> {
-    id: bigint = -1n
-}
 
 new User().id