Rabban Gamliel says: There is no [validity to] a bill of divorce after a bill of divorce, nor [to] maamar after maamar, nor [to] cohabitation after cohabitation, nor [to] chalitzah after chalitzah. The Sages [however] say: There is [validity to] a bill of divorce after a bill of divorce, and [to] maamar after maamar; but after cohabitation or after chalitzah there is nothing.