Okla. Stat. tit. 58, § 58-503: Hearing

At the time and place appointed for the hearing, or at such

other time to which the same may be postponed, upon satisfactory

proof, by affidavit or otherwise, of proper mailing and publication

of notice, as required by the preceding sections, the court shall

conduct said hearing, and the heirs at law, devisees and legatees of

the decedent and all persons interested in the estate, may appear

and contest such application, and the court may examine, under oath,

the applicant and all other persons who come before the court for

that purpose.