reserve x,y for object,X,Y for set;
reserve M for Pnet;

theorem
  X misses Y implies the carrier of PTempty_f_net(X,Y) = X &
  the carrier' of PTempty_f_net(X,Y) = Y &
    Flow PTempty_f_net(X,Y) = {}
proof
  assume X misses Y;
  then PTempty_f_net(X,Y) = PT_net_Str (# X, Y, {}(X,Y), {}(Y,X) #) by Def1;
  hence thesis;
end;
