for i, j being Nat st [i,j] in Indices (n,n --> (- 1)) holds
(n,n --> (- 1)) * i,j <= 0 by MATRIX_2:1;
hence for b₁ being Matrix of n, REAL st b₁ = n,n --> (- 1) holds
b₁ is Nonpositive by Def3; :: thesis: verum