For the purpose of this subchapter the following definition shall apply unless the context clearly indicates or requires a different meaning.
COLLATERAL BONDS. Direct obligations of the United States government, direct obligations of the city or direct obligations and bridge revenue bonds of the state, and no other, and in the following proportions: At least 662/3% in market value of the whole of the bonds shall be United States government bonds or United States treasury notes.
('83 Code, § 36.10)