根据镜像原则,承诺必须严格地与要约相符,受要约人不得进行任何限制、扩张或者变更,否则合同就不能成立。根据实质性变更原则,即使受要约人对要约进行了添加、限制或其它更改,只要这些变动是非实质性的,那么合同仍可宣告成立。而根据《美国统一商法典》的相关规定,无论受要约人是否对要约进行了更改,合同一律可告成立,但既已成立之合同的条款将具有不确定性。 According to the principle of mirroring, the promise must be strictly in line with the offer, subject to no restrictions, expansion or change by the offeree, otherwise the contract can not be established. Under the principle of substantive change, a contract may be declared as insofar as these changes are immaterial even though the offeror has added, restricted or otherwise changed the offer. According to “Uniform Commercial Code of the United States,” the relevant provisions of the contract regardless of whether the offer has been changed, the contract can be formed, but the terms of the contract has been established will be uncertain.