This might seem like a bizarrely specific question to write a whole book about, but that's actually the charm. It covers deep and general ideas, such as class field theory and elliptic functions, which are usually only taught to graduate students, but Cox approaches it all from an extremely concrete question which Fermat thought about.
It says how long ago something was said, so you can tell last month
from 2014 without doing the arithmetic. Full and green is recent; it
drains and cools as the date gets older, and empties completely at about
6 years.
5d5 days ago
8mo8 months ago
2yr2 years ago
4yr4 years ago
9yr9 years ago
A striped bar means the date itself is an estimate — the source did
not carry an exact one. An entry with no date at all gets no bar.