let n, m be Nat; :: thesis: for K being Field
for M1, M2 being Matrix of n,m,K holds width M1 = width M2
let K be Field; :: thesis: for M1, M2 being Matrix of n,m,K holds width M1 = width M2
let M1, M2 be Matrix of n,m,K; :: thesis: width M1 = width M2

per cases ( n > 0 or n = 0 ) ;

suppose n > 0 ; :: thesis: width M1 = width M2

then ( width M1 = m & width M2 = m ) by MATRIX_1:24;
hence width M1 = width M2 ; :: thesis: verum

end;

suppose n = 0 ; :: thesis: width M1 = width M2

then ( width M1 = 0 & width M2 = 0 ) by MATRIX_1:23;
hence width M1 = width M2 ; :: thesis: verum

end;

end;