[eternalban]

Thank you.

So that sent me chasing interval arithmetic's history -- https://en.wikipedia.org/wiki/Interval_arithmetic -- and that page is also silent as to where did it come from. But academic.ru has the (surprising to me) answer that none other than Archimedes (not a surprise) used it:

"Interval arithmetic is not a completely new phenomenon in mathematics; it has appeared several times under different names in the course of history.

For example Archimedes calculated lower and upper bounds 223/71 < π < 22/7 in the 3rd century BC. Actual calculations with intervals has neither been as popular as other numerical techniques, nor been completely forgotten."

https://en.academic.ru/dic.nsf/enwiki/1037936