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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 xoscmounts(host_mount):
 """ Cross OS compatible mount dirs """

    callback_lower_drive_letter = lambda pat: pat.group(1).lower()
    host_mount = re.sub(r"^([a-zA-Z])\:", callback_lower_drive_letter, host_mount)
    host_mount = re.sub(r"^([a-z])", "//\\1", host_mount)
    host_mount = re.sub(r"\\", "/", host_mount)
    return host_mount