It is “well known” as in “this was worked out 200 years ago and is a foundational idea for several branches of mathematics and every undergraduate studying scie

It is “well known” as in “this was worked out 200 years ago and is a foundational idea for several branches of mathematics and every undergraduate studying science, mathematics, or engineering learns this several times in multiple classes before the end of college, and readers of a mathematician’s blog post about his new research results can be expected to be well familiar with the idea, and if they aren’t the research will not be meaningful to them anyway”.