theorem Th14:
  for a,i1 holds
    {p: p.i1 = a} is diophantine Subset of n -xtuples_of NAT
proof
  let a be Integer,i1;
  set i2 = the Element of n;
  defpred P[XFinSequence of NAT] means $1.i1 = a;
  defpred Q[XFinSequence of NAT] means 1*($1.i1) = 0 * ($1.i2)+a;
  A1:for p holds P[p] iff Q[p];
  {p: P[p]} = {q: Q[q]} from Eq(A1);
  hence thesis by Th6;
end;
