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 Th22:
  x in rng p implies x..p - 1 is Element of NAT & len p - x..p is
  Element of NAT
proof
  assume x in rng p;
  then 1 <= x..p & x..p <= len p by Th21;
  hence thesis by INT_1:5;
end;
