reserve x for set;

theorem Th2:
  for L1, L2 being non empty 1-sorted st the carrier of L1 = the
carrier of L2 for N1 being NetStr over L1 ex N2 being strict NetStr over L2 st
  the RelStr of N1 = the RelStr of N2 & the mapping of N1 = the mapping of N2
proof
  let L1, L2 be non empty 1-sorted such that
A1: the carrier of L1 = the carrier of L2;
  let N1 be NetStr over L1;
  reconsider f = the mapping of N1 as Function of the carrier of N1, the
  carrier of L2 by A1;
  take NetStr(#the carrier of N1, the InternalRel of N1, f#);
  thus thesis;
end;
