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
  for T being Tree holds (^T)|<*0*> = T
proof
  let T be Tree;
  set p = <*T*>;
A1: len p = 1 by FINSEQ_1:40;
A2: p.1 = T;
  0+1 = 1;
  hence thesis by A1,A2,Th49;
end;
