Replaces the scaffold-mediated definition with the equivalent direct
condition (two color classes contained in opposite-parity BFS layers
from some root) and removes the scaffold definition, 2-colorability
theorem, connectedness lemma, and equivalence proposition that existed
solely to translate between the two formulations. Updates the
refutation proof to invoke the new definition directly.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
didericis
b5a9030b98
