code: @Override
  	public boolean addAll(Collection<? extends BooleanTerm> terms) {
  		boolean modified = false;
  		// a null booleanTerms means that the expression is
  		// already true, so no need to modify it
  		if (terms == null) {
  			modified = booleanTerms != null;
  			booleanTerms = null;
  		} else if (booleanTerms != null) {
  			for (BooleanTerm term : terms) {
  				modified |= add(term);
  			}
  		}
  		return modified;
  	}
docs: Adds the terms to the formula.  Note that if the formula has
  previously been simplified and determined to evaluate to
  true, then adding any terms will have no effect.