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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def is_newer_b(a, bfiles):
 """ check that all b files have been modified more recently than a """

    if isinstance(bfiles, basestring):
        bfiles = [bfiles]

    if not op.exists(a): return False
    if not all(op.exists(b) for b in bfiles): return False

    atime = os.stat(a).st_mtime # modification time
    for b in bfiles:
        # a has been modified since
        if atime > os.stat(b).st_mtime:
            return False
    return True