Return the representation of the first  `n_max` elements in `items`.

def show_some(items:Collection, n_max:int=5, sep:str=','):
    "Return the representation of the first  `n_max` elements in `items`."
    if items is None or len(items) == 0: return ''
    res = sep.join([f'{o}' for o in items[:n_max]])
    if len(items) > n_max: res += '...'
    return res