theorem Th155: :: SHEFFER2:155

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