theorem Th139: :: SHEFFER2:139

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