reserve f for Function;
reserve p,q for FinSequence;
reserve A,B,C for set,x,x1,x2,y,z for object;
reserve k,l,m,n for Nat;
reserve a for Nat;
reserve D for non empty set;
reserve d,d1,d2,d3 for Element of D;

theorem
  for i being Nat for D being set, P being FinSequence of D st 1 <= i &
  i <= len P holds P/.i = P.i
proof
  let i be Nat;
  let D be set, P be FinSequence of D;
  assume 1 <= i & i <= len P;
  then i in dom P by FINSEQ_3:25;
  hence thesis by PARTFUN1:def 6;
end;
