let L be non empty satisfying_Sheffer_1 satisfying_Sheffer_2 satisfying_Sheffer_3 ShefferStr ; :: thesis: for w, p being Element of L holds (p | w) | ((w | w) | p) = p

let w, p be Element of L; :: thesis: (p | w) | ((w | w) | p) = p

w | p = p | w by Th83;

hence (p | w) | ((w | w) | p) = p by Th92; :: thesis: verum

let w, p be Element of L; :: thesis: (p | w) | ((w | w) | p) = p

w | p = p | w by Th83;

hence (p | w) | ((w | w) | p) = p by Th92; :: thesis: verum