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