Fix return value from ISet.add()

src/edu/caltech/cs2/interfaces/ISet.java

      *         element
      */
     public boolean add(E e) {
-        return this.internalDictionary.put(e, new Object()) != null;
+        return this.internalDictionary.put(e, new Object()) == null;
     }
 
 
         return this.internalDictionary.remove(e) != null;
     }
 
-    /**
-     * Removes all of the elements from this set (optional operation).
-     * The set will be empty after this call returns.
-     *
-     * @throws UnsupportedOperationException if the {@code clear} method
-     *         is not supported by this set
-     */
-    public void clear() {
-        throw new UnsupportedOperationException();
-    }
-
     @Override
     public String toString() {
         StringBuilder b = new StringBuilder();