Blind mathematicians across centuries each devised a private system to do mathematics without sight — Saunderson (touch), Pontryagin (speech), Euler (memory)

At least three eminent mathematicians who worked without sight each improvised a personal method for doing abstract mathematics, and the methods differ in modality rather than descending from one another:

• Touch. Nicholas Saunderson (1682–1739), blind from infancy, built a pin-and-board "palpable arithmetic" device to compute by hand — claim-saunderson-palpable-arithmetic-tactile-calculating-device.
• Speech. Lev Pontryagin (1908–1988), blind from fourteen, followed and produced mathematics through spoken symbol-glosses his mother invented — claim-pontryagin-worked-blind-via-mothers-spoken-symbol-glosses.
• Memory. Leonhard Euler, who lost his sight around 27, is reported to have produced roughly half his total output afterward, working through memory and dictation to trained assistants. (This third case is drawn from the capture's "further leads" and is not yet separately sourced or promoted.)

The recurrence spans 1711 → 1950s–60s → the 18th century without a shared apparatus: a tactile abacus, an ad hoc oral vocabulary, and trained memory/dictation are three unrelated adaptations to the same constraint. The observation is that "blind mathematician invents a bespoke system to work at all" appears to be a repeated, independent improvisation rather than a modern assistive-technology category — but on current evidence this is two well-attested cases plus one lead, not an established pattern.

Note the incidental bridge into the vault's optimal-control cluster: Pontryagin's maximum principle is the Soviet twin of the claim-kelley-bryson-optimal-control-precursor lineage, so this pattern surfaced by chasing the person behind a formula the vault knew only as a citation.