theorem Th145: :: SHEFFER2:145

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