diff --git a/src/de/dhbwstuttgart/typeinference/unify/interfaces/IUnify.java b/src/de/dhbwstuttgart/typeinference/unify/interfaces/IUnify.java
index 92dd941d8..1f73b5508 100644
--- a/src/de/dhbwstuttgart/typeinference/unify/interfaces/IUnify.java
+++ b/src/de/dhbwstuttgart/typeinference/unify/interfaces/IUnify.java
@@ -1,5 +1,6 @@
 package de.dhbwstuttgart.typeinference.unify.interfaces;
 
+import java.util.Optional;
 import java.util.Set;
 
 import de.dhbwstuttgart.typeinference.unifynew.Unifier;
@@ -10,5 +11,5 @@ import de.dhbwstuttgart.typinference.unify.model.MPair;
  * @author Florian Steurer
  */
 public interface IUnify {
-	public Set<MPair> unify(Set<MPair> terms);
+	public Optional<Set<MPair>> unify(Set<MPair> terms);
 }
diff --git a/src/de/dhbwstuttgart/typeinference/unifynew/MartelliMontanariUnify.java b/src/de/dhbwstuttgart/typeinference/unifynew/MartelliMontanariUnify.java
index 89e02cbbe..0f626010b 100644
--- a/src/de/dhbwstuttgart/typeinference/unifynew/MartelliMontanariUnify.java
+++ b/src/de/dhbwstuttgart/typeinference/unifynew/MartelliMontanariUnify.java
@@ -11,6 +11,7 @@ import java.util.stream.Collectors;
 import de.dhbwstuttgart.typeinference.unify.interfaces.IUnify;
 import de.dhbwstuttgart.typinference.unify.model.MPair;
 import de.dhbwstuttgart.typinference.unify.model.MPair.PairOperator;
+import de.dhbwstuttgart.typinference.unify.model.PlaceholderType;
 import de.dhbwstuttgart.typinference.unify.model.Type;
 import de.dhbwstuttgart.typinference.unify.model.TypeParams;
 
@@ -21,7 +22,7 @@ import de.dhbwstuttgart.typinference.unify.model.TypeParams;
 public class MartelliMontanariUnify implements IUnify {
 
 	@Override
-	public Set<MPair> unify(Set<MPair> terms) {
+	public Optional<Set<MPair>> unify(Set<MPair> terms) {
 		Queue<MPair> termsQ = new LinkedList<>(terms);
 		Set<MPair> result = new HashSet<>();
 		
@@ -35,7 +36,7 @@ public class MartelliMontanariUnify implements IUnify {
 			Optional<Set<MPair>> optSet = decompose(pair);
 			
 			if(optSet == null)
-				return new HashSet<>(); // Unification failed
+				return Optional.empty(); // Unification failed
 			
 			if(optSet.isPresent()) {
 				termsQ.addAll(optSet.get());
@@ -55,13 +56,16 @@ public class MartelliMontanariUnify implements IUnify {
 				Unifier uni = optUni.get();
 				termsQ = termsQ.stream().map(uni::apply).collect(Collectors.toCollection(LinkedList::new));
 				result = result.stream().map(uni::apply).collect(Collectors.toCollection(HashSet::new));
+				result.add(pair);
 				continue;
 			}
 			
-			// TODO occurs check?
+			// TODO occurs check notwendig?
+			if(!check(pair)) // Occurs-Check
+				return Optional.empty();
 		}
 		
-		return result;
+		return Optional.of(result);
 	}
 	
 	private boolean delete(MPair pair) {
@@ -96,6 +100,9 @@ public class MartelliMontanariUnify implements IUnify {
 		if(lhs.getTypeParams().size() != 0 && rhs.getTypeParams().size() == 0)
 			return Optional.of(new MPair(rhs, lhs, PairOperator.EQUALSDOT));
 		
+		if(!(lhs instanceof PlaceholderType) && (rhs instanceof PlaceholderType))
+			return Optional.of(new MPair(rhs, lhs, PairOperator.EQUALSDOT));
+		
 		return Optional.empty();
 	}
 	
diff --git a/src/de/dhbwstuttgart/typeinference/unifynew/Unifier.java b/src/de/dhbwstuttgart/typeinference/unifynew/Unifier.java
index 0428a84ef..db821905e 100644
--- a/src/de/dhbwstuttgart/typeinference/unifynew/Unifier.java
+++ b/src/de/dhbwstuttgart/typeinference/unifynew/Unifier.java
@@ -40,4 +40,10 @@ public class Unifier implements Function<Type, Type> {
 	public Type getTarget() {
 		return target;
 	}
+	
+	@Override
+	public String toString() {
+		return source.toString() + " -> " + target.toString();
+	}
 }
+
diff --git a/test/unify/StandardUnifyTest.java b/test/unify/StandardUnifyTest.java
new file mode 100644
index 000000000..41aff15f8
--- /dev/null
+++ b/test/unify/StandardUnifyTest.java
@@ -0,0 +1,74 @@
+package unify;
+
+import java.util.HashSet;
+import java.util.Set;
+
+import junit.framework.Assert;
+
+import org.junit.Test;
+
+import de.dhbwstuttgart.typeinference.unify.interfaces.IUnify;
+import de.dhbwstuttgart.typeinference.unifynew.MartelliMontanariUnify;
+import de.dhbwstuttgart.typinference.unify.model.MPair;
+import de.dhbwstuttgart.typinference.unify.model.Type;
+import de.dhbwstuttgart.typinference.unify.model.MPair.PairOperator;
+
+public class StandardUnifyTest {
+	
+	@Test
+	public void testUnify() {
+		IUnify unify = new MartelliMontanariUnify();
+		TypeFactory tf = new TypeFactory();
+		
+		/*
+		 * Positive Tests
+		 */
+		
+		Type x = tf.getPlaceholderType("x");
+		Type y = tf.getPlaceholderType("y");
+		Type z = tf.getPlaceholderType("z");
+		Type f = tf.getSimpleType("f", x);
+		
+		// {x =. z, f<x> = y}
+		Set<MPair> terms = new HashSet<MPair>();
+		terms.add(new MPair(x, z, PairOperator.EQUALSDOT));
+		terms.add(new MPair(f, y, PairOperator.EQUALSDOT));
+		
+		System.out.println(unify.unify(terms).get());
+		
+		// {f<g<x>,x> = f<y,a>}
+		Type g = tf.getSimpleType("g", "x");
+		Type f1 = tf.getSimpleType("f", g, x);
+		Type a = tf.getExtendsType(tf.getPlaceholderType("a"));
+		Type f2 = tf.getSimpleType("f", y, a);
+		
+		terms = new HashSet<>();
+		terms.add(new MPair(f1, f2, PairOperator.EQUALSDOT));
+		
+		System.out.println(unify.unify(terms).get());
+		
+		/*
+		 * Negative Tests
+		 */
+		
+		// {f(x) =. x}
+		f = tf.getSimpleType("f", x);
+		terms = new HashSet<>();
+		terms.add(new MPair(f, x, PairOperator.EQUALSDOT));
+		Assert.assertFalse(unify.unify(terms).isPresent());
+		
+		// {f(x) =. f(x,y)}
+		f1 = tf.getSimpleType("f", "x");
+		f2 = tf.getSimpleType("f", "x", "y");
+		terms = new HashSet<>();
+		terms.add(new MPair(f1, f2, PairOperator.EQUALSDOT));
+		Assert.assertFalse(unify.unify(terms).isPresent());
+		
+		// {f(x) =. g(x)}
+		f1 = tf.getSimpleType("f", "x");
+		f2 = tf.getSimpleType("g", "x");
+		terms = new HashSet<>();
+		terms.add(new MPair(f1, f2, PairOperator.EQUALSDOT));
+		Assert.assertFalse(unify.unify(terms).isPresent());
+	}
+}