Watch the recursive split tree grow downward, then see sorted subarrays merge back up level by level.

See each comparison as a branch in a decision tree — left for smaller, right for larger, until found or eliminated.

Step through all 7 sub-matrix multiplications that replace the naive 8, and watch the result matrix assemble.

Geometric D&C: divide the point set by a vertical line, recurse on halves, then check the δ-wide strip for cross-half pairs.