The question is given in the given figure.

x. Problem Solving Solve the following problem and give the proof of correctness for the same. (Hint: check the pre-conditions and post-conditions), Problem: There are four people who want to cross a rickety bridge. They all begin on the same side. You have 17 minutes to get them all across to the other side. It is night time and they have one flash light. A maximum of two people can cross the bridge at one time. Any part that crosses, Citaor one or two people, must have the flash light with them. The flash light must be walked back and forth. It cannot be thrown. Person A takes 1 minute to cross the bridge, Persons B, C and D take 2, 5 and 10 minutes respectively. A pair must walk together at the rate of the slower person's pace