In 1977, the Supreme Court's Coker v. Georgia decision barred the death penalty for rape of an adult woman, and implied that the death penalty was inappropriate for any offense against another person other than murder. Prior to the decision, the death penalty for rape of an adult had been gradually phased out in the United States, and at the time of the decision, the State of Georgia and the U.S. Federal government were the only two jurisdictions to still retain the death penalty for that offense. However, three states maintained the death penalty for child rape, as the Coker decision only imposed a ban on executions for the rape of an adult woman. In 2008, the Kennedy v. Louisiana decision barred the death penalty for child rape. The result of these two decisions means that the death penalty in the United States is largely restricted to cases where the defendant took the life of another human being. The current federal kidnapping statute, however, may be exempt because the death penalty applies if the victim dies in the perpetrator's custody, not necessarily by his hand, thus stipulating a resulting death, which was the wording of the objection. In addition, the Federal government retains the death penalty for non-murder offenses that are considered crimes against the state, including treason, espionage, and crimes under military jurisdiction.

Answer this question, if possible (if impossible, reply "unanswerable"): For what offense did Coker v. Georgia forbid the death penalty?
rape of an adult woman