def METHOD_NAME(fil, pre='', post=''):
    """Function to locate a file *pre* + *fil* + *post* in any possible
    lettercase permutation of *fil*. Returns *pre* + *fil* + *post* if
    available, None if not.
    """
    afil = None
    for per in list(all_casings(fil)):
        if os.path.isfile(pre + per + post):
            afil = pre + per + post
            break
        else:
            pass
    return afil