Section 13.12.514 - Contracts concerning succession(a) A contract to make a will or devise, or not to revoke a will or devise, or to die intestate, if executed after January 1, 1997, may be established only by (1) provisions of a will stating material provisions of the contract;(2) an express reference in a will to a contract and extrinsic evidence proving the terms of the contract; or(3) a writing signed by the decedent evidencing the contract.(b) The execution of a joint will or mutual wills does not create a presumption of a contract not to revoke the will or wills.