Subject to the provisions of section 15-103, the obligee's release or discharge of one or more of several obligors, or of one or more of joint, or of joint and several obligors shall not discharge co-obligors, against whom the obligee in writing and as part of the same transaction as the release or discharge, expressly reserves his rights; and in the absence of such a reservation of rights shall discharge co-obligors only to the extent provided in section 15-105.
New York Legal Code