theorem Th130: :: SHEFFER2:130

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