diff --git a/src/main/java/ab1/impl/GRUPPE/NFAImpl.java b/src/main/java/ab1/impl/GRUPPE/NFAImpl.java
index 126069c..2b2b352 100644
--- a/src/main/java/ab1/impl/GRUPPE/NFAImpl.java
+++ b/src/main/java/ab1/impl/GRUPPE/NFAImpl.java
@@ -47,7 +47,7 @@ public class NFAImpl implements NFA {
     public void addTransition(Transition transition) throws FinalizedStateException {
         if (this.isFinalized) {
             throw new FinalizedStateException();
-        } else {
+        } else if (!this.transitions.contains(transition)) {
             this.transitions.add(transition);
         }
     }
@@ -56,7 +56,7 @@ public class NFAImpl implements NFA {
     public void addAcceptingState(String state) throws FinalizedStateException {
         if (this.isFinalized) {
             throw new FinalizedStateException();
-        } else {
+        } else if (!this.states.contains(state)) {
             this.acceptingStates.add(state);
         }
     }
@@ -80,7 +80,6 @@ public class NFAImpl implements NFA {
     }
      */
 
-
     // #TODO
     @Override
     public NFA union(NFA other) throws FinalizedStateException {
@@ -99,16 +98,17 @@ public class NFAImpl implements NFA {
         return null;
     }
 
+
     // #TODO
     @Override
     public NFA kleeneStar() throws FinalizedStateException {
-        if (this.isFinalized) {
+        if (!this.isFinalized) {
             throw new FinalizedStateException();
         }
 
         NFAImpl nfa = new NFAImpl(this.initialState);
 
-        // deep copy but without accepting states
+        // copy, but without accepting states
         nfa.states.addAll(this.states);
         nfa.transitions.addAll(this.transitions);
 
@@ -119,24 +119,22 @@ public class NFAImpl implements NFA {
             nfa.transitions.add(loopBackTransition);
         }
 
-        // adding the initial state as accepting state
+        // adding the initial state as accepting state because we have to accept the empty string
         nfa.acceptingStates.add(this.initialState);
 
-        nfa.finalizeAutomaton();
-
         return nfa;
     }
 
     // #TODO
     @Override
     public NFA plusOperator() throws FinalizedStateException {
-        if (this.isFinalized) {
+        if (!this.isFinalized) {
             throw new FinalizedStateException();
         }
 
         NFAImpl nfa = new NFAImpl(this.initialState);
 
-        // simple deep copy
+        // simple copy
         nfa.states.addAll(this.states);
         nfa.transitions.addAll(this.transitions);
         nfa.acceptingStates.addAll(this.acceptingStates);
@@ -158,13 +156,11 @@ public class NFAImpl implements NFA {
         return null;
     }
 
-    // #TODO
     @Override
     public boolean isFinalized() {
         return isFinalized;
     }
 
-    // #TODO
     @Override
     public void finalizeAutomaton() {
         this.isFinalized = true;
@@ -179,7 +175,8 @@ public class NFAImpl implements NFA {
 
     // #TODO
     @Override
-    public boolean acceptsWord(String word) {
+    public boolean acceptsWord(String word) throws FinalizedStateException {
+        //check if word is accepted
         return false;
     }
 }