diff --git a/src/main/java/de/neemann/digital/analyse/expression/Not.java b/src/main/java/de/neemann/digital/analyse/expression/Not.java
index 4918ea2aa..25c106093 100644
--- a/src/main/java/de/neemann/digital/analyse/expression/Not.java
+++ b/src/main/java/de/neemann/digital/analyse/expression/Not.java
@@ -10,7 +10,8 @@ public final class Not implements Expression {
     private Expression expression;
 
     /**
-     * Creates a not expression
+     * Creates a not expression.
+     * Simplifies the expression if possible.
      *
      * @param a the child expression to invert
      * @return the inverted expression
@@ -27,6 +28,12 @@ public final class Not implements Expression {
             return new Not(a);
     }
 
+    /**
+     * Creates a new instance.
+     * In most cases it's better to use {@link Not#not(Expression)}.
+     *
+     * @param expression
+     */
     public Not(Expression expression) {
         this.expression = expression;
     }
diff --git a/src/main/java/de/neemann/digital/draw/builder/Builder.java b/src/main/java/de/neemann/digital/draw/builder/Builder.java
index d27760e0e..7d370e263 100644
--- a/src/main/java/de/neemann/digital/draw/builder/Builder.java
+++ b/src/main/java/de/neemann/digital/draw/builder/Builder.java
@@ -152,14 +152,14 @@ public class Builder {
         for (FragmentVariable f : fragmentVariables) {
             Vector p = f.getCircuitPos();
             int in = varPos.get(f.getVariable().getIdentifier());
-            if (f.isNeg()) in += SIZE;
+            if (f.isInvert()) in += SIZE;
             circuit.add(new Wire(p, new Vector(in, p.y)));
         }
     }
 
     private boolean isNotNeeded(String identifier) {
         for (FragmentVariable fv : fragmentVariables)
-            if (fv.isNeg() && fv.getVariable().getIdentifier().equals(identifier))
+            if (fv.isInvert() && fv.getVariable().getIdentifier().equals(identifier))
                 return true;
 
         return false;
diff --git a/src/main/java/de/neemann/digital/draw/builder/FragmentVariable.java b/src/main/java/de/neemann/digital/draw/builder/FragmentVariable.java
index c15d50c73..0a3490f03 100644
--- a/src/main/java/de/neemann/digital/draw/builder/FragmentVariable.java
+++ b/src/main/java/de/neemann/digital/draw/builder/FragmentVariable.java
@@ -8,17 +8,25 @@ import java.util.ArrayList;
 import java.util.List;
 
 /**
+ * Represents a variable
+ *
  * @author hneemann
  */
 public class FragmentVariable implements Fragment {
     private final Variable variable;
-    private final boolean neg;
+    private final boolean invert;
     private Vector pos;
     private Vector circuitPos;
 
-    public FragmentVariable(Variable variable, boolean neg) {
+    /**
+     * Creates a new variable
+     *
+     * @param variable the variable
+     * @param invert   true if variable needs to be inverted
+     */
+    public FragmentVariable(Variable variable, boolean invert) {
         this.variable = variable;
-        this.neg = neg;
+        this.invert = invert;
     }
 
     @Override
@@ -36,12 +44,18 @@ public class FragmentVariable implements Fragment {
         circuitPos = pos.add(this.pos);
     }
 
+    /**
+     * @return the position of the variable in the circuit
+     */
     public Vector getCircuitPos() {
         return circuitPos;
     }
 
-    public boolean isNeg() {
-        return neg;
+    /**
+     * @return true if variable is inverted
+     */
+    public boolean isInvert() {
+        return invert;
     }
 
     @Override
@@ -56,6 +70,9 @@ public class FragmentVariable implements Fragment {
         return o;
     }
 
+    /**
+     * @return the variable
+     */
     public Variable getVariable() {
         return variable;
     }