code: @Override
  	public void clear() {
  		// This makes the formula false
  		if (booleanTerms != null) {
  			booleanTerms.clear();
  		} else {
  			booleanTerms = new HashSet<BooleanTerm>();
  		}
  		isSimplified = true;
  	}
docs: /* (non-Javadoc)
  @see java.util.Set#clear()