The complaining party must prove that the contract is valid and that it has suffered damage as a result of the infringement. In more complex situations, such as multinational trade negotiations, a bilateral treaty can be what is called a “side deal”. In other words, both sides are involved in the general negotiations, but may also see the need for a separate treaty that only concerns their common interests. For an acceptance to be valid, it must normally be identical to the offer.  This is usually called the reflection rule. If the acceptance is not a reflection of the offer, it is considered a refusal and a counter-offer that can be accepted by the original supplier. For example, Eric asks, “Dan, will you agree to paint my fence blue for $150?” and Dan answers, “Green is a better color.