theorem Th157: :: SHEFFER2:157

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