The heretofore unverified but practically applied in cartography conjecture that no more than four colours are needed to distinguish bordering regions on a map was announced as proven on this day in 1976 after more than century since it was first proposed by two mathematicians at the the University of Illinois Urbana-Champaign campus. Not feasible to perform the brute calculation by hand, this topology problem (see previously) was solved with the aid of a supercomputer, the first instance of a technical assist for a math problem, the claim rejected by some peers at the time because they couldn’t check the work.
synchronoptica
one year ago: arriving in Morbihan (with synchronoptica)
two years ago: Putin and Kim hold a summit, the premiere of Evita plus the estate of Jim Henson selling off its Hollywood lot
three years ago: California v Miller plus assorted links worth the revisit
four years ago: pioneering parachutist Tiny Broadwick (1913), Texas v Johnson plus more links to enjoy
five years ago: the Stonehenge Free Festival (1974), the introduction of the LP record (1948) plus Return to Oz (1985)
six years ago: a CNN competitor (1982), EU proposes a digital services tax, remixing the Bayeux tapestry, setting the record straight, AI-generated perfumes plus Internation Yoga Day