for K being Field
for M being Matrix of K holds
( the_rank_of M = 1 iff ( ex i, j being Nat st
( [i,j] in Indices M & M * (i,j) <> 0. K ) & ( for i0, j0, n0, m0 being non zero Nat st i0 <> j0 & n0 <> m0 & [:{i0,j0},{n0,m0}:] c= Indices M holds
Det (EqSegm (M,{i0,j0},{n0,m0})) = 0. K ) ) )