What is the difference between the following sentences:
We have no jobs at present, but if the situation should change, we will contact you.
We have no jobs at present, but if the situation changes, we will contact you.
We have no jobs at present, but if the situation is to change, we will contact you.
Sentences 1 and 2 I took from Murphy, where they say the first one means that the situation is less likely to change.