reserve i,j,k,l for natural Number;
reserve A for set, a,b,x,x1,x2,x3 for object;
reserve D,D9,E for non empty set;
reserve d,d1,d2,d3 for Element of D;
reserve d9,d19,d29,d39 for Element of D9;
reserve p,q,r for FinSequence;

theorem Th12:
  <*d1,d2,d3*> is FinSequence of D
proof
  rng <*d1,d2,d3*> = {d1,d2,d3} by Lm2;
  hence thesis by FINSEQ_1:def 4;
end;
