mathlib

b30f25ce - fix(data/set/prod): fix the way `×ˢ` associates (#12943)

fix(data/set/prod): fix the way `×ˢ` associates (#12943) Previously `s ×ˢ t ×ˢ u` was an element of `set ((α × β) × γ)` instead of `set (α × β × γ) = set (α × (β × γ))`.