(a) A will or codicil, or a part thereof, may not be revoked, except by implication of law, otherwise than by
(1) a later will, codicil, or other writing declaring the revocation, executed as provided by section 18-103 or 18-107; or
(2) burning, tearing, cancelling, or obliterating the will or codicil, or the part thereof, with the intention of revoking it, by the testator himself, or by a person in his presence and by his express direction and consent.
(b) A will or codicil, or a part thereof, after it is revoked, may not be revived otherwise than by its re-execution, or by a codicil executed as provided in the case of wills, and then only to the extent to which an intention to revive is shown.