reserve a,b,c,d,m,x,n,j,k,l for Nat,
  t,u,v,z for Integer,
  f,F for FinSequence of NAT;
reserve p,q,r,s for real number;
reserve a,b,c,d,m,x,n,k,l for Nat,
  t,z for Integer,
  f,F,G for FinSequence of REAL;
reserve q,r,s for real number;
reserve D for set;

theorem Th10:
  for f be FinSequence of REAL st n in dom f holds len(f|n) = n
  proof
    let f be FinSequence of REAL;
    assume n in dom f; then
    n <= len f by FINSEQ_3:25;
    hence thesis by FINSEQ_1:59;
  end;
