<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def prep_samples(*items):
 """Handle any global preparatory steps for samples with potentially shared data. Avoids race conditions in postprocess alignment when performing prep tasks on shared files between multiple similar samples. Cleans input BED files to avoid issues with overlapping input segments. """

    out = []
    for data in (utils.to_single_data(x) for x in items):
        data = cwlutils.normalize_missing(data)
        data = cwlutils.unpack_tarballs(data, data)
        data = clean_inputs(data)
        out.append([data])
    return out