Gee, I hope Bonnie didn't claim they were original. Certainly it's not
difficult to figure out.

More interesting to me is recent work on letting a delta-sigma ADC
sample at a rate to serve as a direct IF sampler--up around 5GHz. The
practice of getting it to work really right at such frequencies is much
more interesting than the formulas for what frequencies work and avoid
aliasing.

Cheers,
Tom