let n, m be Nat; :: thesis: for K being non empty set
for M1, M2 being Matrix of n,m,K holds width M1 = width M2
let K be non empty set ; :: 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 A1: n > 0 ; :: thesis: width M1 = width M2

then width M1 = m by MATRIX_0:23;
hence width M1 = width M2 by A1, MATRIX_0:23; :: thesis: verum

end;

suppose A2: n = 0 ; :: thesis: width M1 = width M2

then width M1 = 0 by MATRIX_0:22;
hence width M1 = width M2 by A2, MATRIX_0:22; :: thesis: verum

end;

end;