Okla. Stat. tit. 70, § 70-2207: Approval of bonds - Incontestability

All bonds issued hereunder shall have on the backs thereof the

certificate required by Section 29 of Article X of the Constitution

of Oklahoma. Such bonds shall be submitted to the Attorney General

of Oklahoma for his examination and when such bonds have been

examined and certified as legal obligations by the Attorney General,

in accordance with such requirements as he may make, shall be

incontestable in any court in the State of Oklahoma unless suit

thereon shall be brought in a court having jurisdiction thereof

within thirty (30) days from the date of such approval. Bonds so

approved by the Attorney General shall be prima facie valid and

binding obligations according to their terms, and the only defense

which may be offered thereto in any suit instituted after such

thirty-day period shall have expired shall be forgery, fraud, or

violation of the Constitution.