We were playing bridge the other evening. My sister Alice was dealing, and she had dealt about half the cards when her mobile phone rang. She put down the undealt cards, excused herself, and left the table to answer the phone. When she returned no one could remember where the last card had been dealt. None of the cards had been touched. Alice thought for a moment, and then she completed the deal rapidly and accurately, giving each player exactly the same cards he would have received if there'd been no interruption. How?