[Retros] Dual avoidance

[afretro]

Dear Andrew,
Thanks a lot for the dedication! Your 9-move sequence leading to hg1=S# is very nice-looking indeed.
Hirokaz▓s idea might be reformulated as ⌠dual-avoidance on the final move of a SPG ending in mate through pawn promotion.■

> There is still the question of producing a promotion to R or B which works

> as a PG, where the promotion to Q has a single dual.

It is unclear how this can be achieved. It requires making a SPG with 2 solutions one of which ends in mate through queening.
Many thanks again.
Best,
Andrey