reserve x,y,z for object,X,Y for set;
reserve N for e_net;

theorem Th14:
  dom (the entrance of N) c= the carrier of N & rng (the entrance
  of N) c= the carrier of N & dom (the escape of N) c= the carrier of N & rng (
  the escape of N) c= the carrier of N
proof
  the entrance of N c= [:the carrier of N,the carrier of N:] & the escape
  of N c= [:the carrier of N,the carrier of N:] by Def1;
  hence thesis by SYSREL:3;
end;
