theorem Th93: :: SHEFFER2:93

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