26 USC 752 - Treatment of certain liabilities

(a) Increase in partner’s liabilities 
Any increase in a partners share of the liabilities of a partnership, or any increase in a partners individual liabilities by reason of the assumption by such partner of partnership liabilities, shall be considered as a contribution of money by such partner to the partnership.
(b) Decrease in partner’s liabilities 
Any decrease in a partners share of the liabilities of a partnership, or any decrease in a partners individual liabilities by reason of the assumption by the partnership of such individual liabilities, shall be considered as a distribution of money to the partner by the partnership.
(c) Liability to which property is subject 
For purposes of this section, a liability to which property is subject shall, to the extent of the fair market value of such property, be considered as a liability of the owner of the property.
(d) Sale or exchange of an interest 
In the case of a sale or exchange of an interest in a partnership, liabilities shall be treated in the same manner as liabilities in connection with the sale or exchange of property not associated with partnerships.