semi-open codes

We will show that a system is synchronized if and only if it has a cover whose covermap is semi-open. also, any factor code on an irreducible soc shift is semi-open and theimage of a synchronized system by a semi-open code is synchronized. on the other side,right-closing semi-open extension of an irreducible shift of nite type is of nite type.moreover, we show that any semi-open code on a synchronized system is bi-continuing a.e.