Two mathematicians were jailed for running an illegal casino. Their punishment was supposed to be as follows:
Each morning, they will each bet on one side of a coin, after which a prison guard flips a coin.
If either of them wins the bet, they both live to the next day, otherwise they will be executed.
If they are going to stay alive for two weeks, they will go free.

The first morning, they called for the king and made the following deal:
The term will be extended from two weeks to two years.
They will each bet on the other one's coin, after they could see the result of their own coin.

Why did they make the deal?