theorem Th98: :: SHEFFER2:98

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