theorem Th84: :: SHEFFER2:84

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