reserve x,y,z for object,
  i,j,n,m for Nat,
  D for non empty set,
  s,t for FinSequence,
  a,a1,a2,b1,b2,d for Element of D,
  p, p1,p2,q,r for FinSequence of D;
reserve M,M1,M2 for Matrix of D;

theorem Th25:
  for M being Matrix of n,m,D holds len M = n & Indices M = [:Seg
  n,Seg width M:]
proof
  let M be Matrix of n,m,D;
  len M = n by Def2;
  hence thesis by FINSEQ_1:def 3;
end;
