Rikai

Why another textbook site

When a textbook loses you, it is usually because of what it did not write: the three lines hidden behind “clearly”, the step that silently used an unstated hypothesis, the theorem whose purpose is never explained. Rikai writes those parts down.

Gaps filled in

Every proof step says which hypothesis and which earlier result it uses. Nothing is left to “it is easy to see”.

Copy the math

Hover any formula to copy its LaTeX source, or copy a whole article as Markdown.

The English edition is being translated from the Japanese one. The Japanese site currently has the full catalogue.