theorem Th115: :: SHEFFER2:115

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