<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def remap_index_fn(ref_file):
 """Map sequence references to equivalent star indexes """

    return os.path.join(os.path.dirname(os.path.dirname(ref_file)), "star")