Complex sentence: Lastly, Chudnovsky, Edwards, and Paul Seymour have attempted to prove nine-regular planar graphs are edge colourable, but were unable to because it appears to be much more difficult that the eight-regular case.
Split into simpler sentences: Lastly, Chudnovsky, Edwards, and Paul Seymour have attempted to prove nine-regular planar graphs are edge colourable. They have yet to accomplish this because it appears to be much more difficult that the eight-regular case.