@Override
	public boolean equals(Object object) {
		if ( object == null) 			        return false;		
		if ( object == this )                   return true;
		if ( !(object instanceof Operation) )	return false;
		
		Operation expression = (Operation) object;
		return     expression.operator == this.operator 
				&& expression.left.equals(this.left) 
				&& expression.right.equals(this.right);
	}