<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _zom_index(lexer):
 """Return zero or more indices."""

    tok = next(lexer)
    # ',' INT
    if isinstance(tok, COMMA):
        first = _expect_token(lexer, {IntegerToken}).value
        rest = _zom_index(lexer)
        return (first, ) + rest
    # null
    else:
        lexer.unpop_token(tok)
        return tuple()