theorem Th73: :: SHEFFER2:73

for L being non empty satisfying_Sheffer_1 satisfying_Sheffer_2 satisfying_Sheffer_3 ShefferStr
for q, p, y, w being Element of L holds ((w | (y | (y | y))) | p) | ((q | q) | p) = (p | (w | q)) | (p | (w | q))