The proceeds and investments in the “refunding fund” shall be in an amount sufficient to meet either the requirements of paragraph (a) or paragraph (b) at the time of issuance of the refunding bonds, as certified by a certified public accountant licensed to practice in this state.
(a) The proceeds and investments, together with any interest or other gain to be derived from any such investment, shall be in an amount sufficient to pay the principal, interest, and redemption premiums, if any, on the refunded bonds as they become due or at designated dates prior to maturity and the designated costs of issuance of the refunding bonds.
(b) The proceeds and investments, together with any interest or other gain to be derived from any such investment, shall be in an amount sufficient to pay the principal, interest, and redemption premiums, if any, on the refunding bonds prior to the maturity of the bonds to be refunded or prior to a designated date or dates before the maturity of the bonds to be refunded, the principal and any redemption premiums due on the refunded bonds at maturity or upon that designated date or dates, and the designated costs of issuance of the refunding bonds.