:: deftheorem Def2 defines - MATRIX_3:def 2 :
for K being Ring
for A, b₃ being Matrix of K holds
( b₃ = - A iff ( len b₃ = len A & width b₃ = width A & ( for i, j being Nat st [i,j] in Indices A holds
b₃ * (i,j) = - (A * (i,j)) ) ) );