theorem Th137: :: SHEFFER2:137

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