  We define class-closing factor codes from shifts of finite type and show that
they are continuing if their images are of finite type. We establish several
relations between class-closing factor codes, continuing factor codes and
constant-class-to-one factor codes. In particular it is shown that a factor
code between irreducible shifts of finite type is constant-class-to-one if and
only if it is bi-class-closing, generalizing a result of Nasu.
