diff --git a/src/Checker.php b/src/Checker.php
index 6183985..88b3f3d 100644
--- a/src/Checker.php
+++ b/src/Checker.php
@@ -14,9 +14,9 @@ class Checker implements CheckerInterface
     /**
      * @inheritdoc
      */
-    public function fulfills($argument1, TypeInterface $requirement)
+    public function fulfills($element, TypeInterface $requirement)
     {
-        return new Result(true, []);
+        return $requirement->check($element);
     }
 
 }
\ No newline at end of file
diff --git a/src/Type/ListType.php b/src/Type/ListType.php
index 1b385ab..cf1364e 100644
--- a/src/Type/ListType.php
+++ b/src/Type/ListType.php
@@ -45,7 +45,7 @@ public function check($value)
         foreach ($value as $item) {
             $result = $this->child->check($item);
 
-            $valid &= $result->isValid();
+            $valid = $valid && $result->isValid();
             $errors += $result->getErrors();
         }
 
diff --git a/src/Type/ObjectType.php b/src/Type/ObjectType.php
index d67b5a9..ae32168 100644
--- a/src/Type/ObjectType.php
+++ b/src/Type/ObjectType.php
@@ -40,7 +40,7 @@ public function check($value)
             }
 
             $result = $child->check($value[$key]);
-            $valid &= $result->isValid();
+            $valid = $valid && $result->isValid();
             $errors += $result->getErrors();
         }