Sole Prime Differencedoku
Much like the sum variant, the type of clues in this puzzle depend on whether or not there is a single prime between two entries. Any numeric clue between cells indicates that exactly one of the numbers in those cells is prime and also reveals the difference (larger minus smaller) of the two numbers. A numberless clue indicates that either both or neither of the cells contain primes.
The first example has been completed as an aid. I am including larger versions of each of the three individual puzzles below, together with a PDF version and the solutions.