theorem Th48:
  accessibleStates tfsm c= the carrier of tfsm & for q holds q in
  accessibleStates tfsm iff q is accessible
proof
  set AS = { q where q is State of tfsm: q is accessible };
  AS c= the carrier of tfsm
  proof
    let x be object;
    assume x in AS;
    then ex q being State of tfsm st x = q & q is accessible;
    hence thesis;
  end;
  hence accessibleStates tfsm c= the carrier of tfsm;
  let q be State of tfsm;
  hereby
    assume q in accessibleStates tfsm;
    then ex q9 being State of tfsm st q9 = q & q9 is accessible;
    hence q is accessible;
  end;
  thus thesis;
end;
