The contract to act on those occasions becomes void.

Reciprocal promise to do things legal, and also other things illegal Reciprocal promise to do things legal, and also other things illegal.—Where persons reciprocally promise, firstly, to do certain things which are legal, and secondly, under specified circumstances to do certain other things which are illegal, the first set up promises is a contract, but the second is-a void agreement.

Illustration. A and B agree that A shall sell B a house for 10,000 rupees, but that, if B uses it as a gambling house, he shall pay A,50,000 rupees for it. The first set of reciprocal promises, namely, to sell the house and to pay 10,000 rupees for it, is a contract.