premise: The obligations in this agreement shall not apply to Proprietary Information: a) which at the time of circulation has already entered the public domain or which after circulation enters the public domain (other than through a breach of this agreement); b) which at the time of circulation is already known by the receiving party (as evidenced in writing) and is not hindered by any obligation not to circulate; c) which is later acquired by the receiving party from another source and is not hindered by any obligation not to circulate;