(a) A revocation may be express or implied.
(b) An express revocation occurs when the testator by writing or action expressly annuls a will. An express revocation takes effect instantly.
(c) An implied revocation results from the execution of a subsequent inconsistent will that does not by its terms expressly revoke the previous will. An implied revocation takes effect only when the subsequent inconsistent will becomes effective. If the subsequent inconsistent will fails to become effective from any cause, the implied revocation is not completed.