reserve a,x,y for object, A,B for set,
  l,m,n for Nat;
reserve X,Y for set, x for object,
  p,q for Function-yielding FinSequence,
  f,g,h for Function;
reserve m,n,k for Nat, R for Relation;

theorem Th69:
  iter(R,1) = R
proof
  thus iter(R,1) = iter(R,0+1)
    .= R*iter(R,0) by Th68
    .= R*id(field R) by Th67
    .= R by Lm3;
end;
