5 · Compute a boundary quotient

Compactly supported pushforward compares functions near the boundary with functions defined everywhere. A line and a coordinate cross give small models of this quotient.

Try this. Use the same truncation for both shapes. The line keeps one tail. The cross keeps a tail from each branch and one extra contribution from the relation at their shared point.

Remark 8.5 gives the exact dualizing-complex formula for the cross. This activity checks only the ranks of finite truncations and identifies the extra contribution from the crossing relation.