It's one of the most trivial library functions ever:
(define (square x) (* x x))
The request gave the (weak) reason that it could have an optimized method for bignums, but voter comments suggest they were more interested in symmetry with
sqrt. They also added
make-list for symmetry with
make-vector. I don't think symmetry is a good reason in either case, let alone sufficient reason to add features to Small Scheme, but
square is attractive as a convenience.
It's not the most important feature (and it probably belongs in Big Scheme, not Small Scheme), but it's a small step forward. Every language that aims to be convenient should have
square in its standard library.