reserve x,y,z for object, X,Y for set,
  i,k,n for Nat,
  p,q,r,s for FinSequence,
  w for FinSequence of NAT,
  f for Function;

theorem Th28:
  <*x*> is Tree-yielding iff x is Tree
proof
A1: x is Tree iff {x} is constituted-Trees by Th12;
  rng <*x*> = {x} by FINSEQ_1:39;
  hence thesis by A1;
end;
