When summarized the chapter 2, the author mentioned that
"Specifically, a 200-digit number is raised to a large power (usually another 200-digit number), with only the low 200 or so digits retained after each multiplication."
Q:What is this mean? P.S:My English is a little bad.
If we replace 200 with 3, it would mean something like computing 123^456, but only retaining the low 3 digits (the ones, tens and hundreds places), mathematically equivalent to (123^456)%1000.