theorem Th73:
  for X being Subset of HFuncs(NAT) st X is primitive-recursively_closed
  holds PrimRec c= X
proof
  let X be Subset of HFuncs(NAT);
  set S = { R where R is Subset of HFuncs(NAT) : R is
  primitive-recursively_closed };
  assume X is primitive-recursively_closed;
  then
A1: X in S;
  let x be object;
  assume x in PrimRec;
  hence thesis by A1,SETFAM_1:def 1;
end;
