"The most powerful diagram in mathematics" —
The YouTube lecturer is not referring to the Fano plane diagram cited
in the AI Overview below, but to a much more sophisticated figure,
the Miracle Octad Generator (MOG) of R. T. Curtis.
Some context —
A rearrangement of the Miracle Octad Generator —
The diagram below may be less powerful , but it illustrates a result that,
although less miraculous , is perhaps more historically significant —
