Using PMI, prove the following holds: 3n1 is a multiple of 2

The factorial function can be defined as:

factorial (0) = 1

factorial (n) = n * factorial (n - 1)

Write a recursive function for factorial, preserving the PMI steps - i.e., the basis step, followed by the inductive step.

[You could write the function in a pseudo-code, C++ or Java]