53a9192f65
Remove the flip-symmetric definition, the class $\mathcal{F}$, and
all references to flip-symmetry from the abstract, motivation, and
section 3 title. Section 3 is renamed to reflect what remains: the
flip neighborhood and the colored edge flip class. The principal
theorem's label is renamed to thm:flip-neighborhood-4colorable to
match its statement.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>