(21,90)→ ¬Y;AND THUS, WE GET A CONTRADICTION AT 90.[12, Y],[19, Y]

90 : - BÁO CÁO TOÁN HỌC FANS AND BUNDLES IN THE GRAPH OF PAIRWISE SUMS AND PRODUCT POTX
Toán BÁO CÁO TOÁN HỌC FANS AND BUNDLES IN THE GRAPH OF PAIRWISE SUMS AND PRODUCT POTX
90: (21,90)→ ¬y;and thus, we get a contradiction at 90.[12, y],[19, y] :