Original: A computer-aided proof produced in 1976 by Kenneth Appel and Wolfgang Haken makes fundamental use of the notion of '' discharging '' developed by Heesch . The proof involved checking the properties of 1,936 configurations by computer , and was not fully accepted at the time due to its complexity .
Simplified: A proof produced in 1976 by Kenneth Appel and Wolfgang Haken , which involved checking the properties of 1,936 configurations by computer , was not fully accepted at the time due to its complexity .