- A P4 is deleted when |z_P4 − z_bar| < (d_P4 + d_bar)/2 against B5 and B1
(the 확대기초 top layer, from the 상면). B11/B12 are not checked (Q-C9 무시).
- The P6 crossties start from the first kept P4.
- Tests: the document's example keeps all 8; B5 moved to −70 deletes the P4 at
−60; a P4 just outside the limit is kept.
Co-Authored-By: Claude Haiku 5.5 <noreply@anthropic.com>