§ 15-105. Discharge of one obligor, without reservation. 1. If an
obligee releasing or discharging an obligor without express reservation
of rights against a co-obligor, then knows or has reason to know that
the obligor released or discharged did not pay so much of the claim as
he was bound by his contract or relation with that co-obligor to pay,
the obligee's claim against that co-obligor shall be satisfied to the
amount which the obligee knew or had reason to know that the released or
discharged obligor was bound to such co-obligor to pay.

2. If an obligee so releasing or discharging an obligor has not then
such knowledge or reason to know, the obligee's claim against the
co-obligor shall be satisfied to the extent of the lesser of two
amounts, namely (a) the amount of the fractional share of the obligor
released or discharged, or (b) the amount that such obligor was bound by
his contract or relation with the co-obligor to pay.