First, you’ll need two utility functions, one to test whether a given number is prime and another that returns the next prime number greater or equal to its argument. In both cases you can use a simple, but inefficient, brute-force approach.

to express a loop that executes the body once each for each prime number greater or equal to 0 and less than or equal to 19, with the variable p holding the prime number. It makes sense to model this macro on the form of the standard and **DOTIMES** macros; macros that follow the pattern of existing macros are easier to understand and use than macros that introduce gratuitously novel syntax.

Now you’re ready to start writing the macro code that will translate from the former to the latter.