Nebraska Revised Statute 14-512
The council shall provide and maintain a sinking fund for the payment of the general bonds of the city and the interest thereon. Such sinking fund shall be maintained from the following sources of revenue: (1) Amounts raised by taxation for that purpose; (2) balances transferred at the end of each fiscal year or biennial period from the several funds provided for in sections 14-501 and 14-502; and (3) such other amounts and sums as may be transferred thereto by the council. Money and credits in the sinking fund shall be held inviolate, shall not be transferred to any other fund, and shall be used for the purpose of paying (a) the interest on the general bonds of the city, (b) maturing bonds of the city, and (c) bonds of the city which may be paid before maturity. The money and credits thereof when not used or needed for the purposes specified in this section may temporarily be invested in registered general warrants of the city or of the school district situated within the city under such conditions as will enable the same to be obtained and available at any time desired for the purposes specified in this section.