After the occupation was over, room for critical thinking was curtailed by more centralised political control. Jorn found this unacceptable and broke with the Danish Communist Party whilst remaining a lifelong communist. He was a founder member of Cobra and was a prime mover of their subsequent merger with the Lettriste Internationale and London Psychogeographical Association to form the Situationist International (S.I.). Here he applied his scientific and mathematical knowledge drawn from Henri Poincaré and Niels Bohr to develop his situlogical technique.
His philosophical system Triolectics was given a practical manifestation through the development of Three sided football.\n