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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 _clauses(lexer, varname, nvars):
 """Return a tuple of DIMACS CNF clauses."""

    tok = next(lexer)
    toktype = type(tok)
    if toktype is OP_not or toktype is IntegerToken:
        lexer.unpop_token(tok)
        first = _clause(lexer, varname, nvars)
        rest = _clauses(lexer, varname, nvars)
        return (first, ) + rest
    # null
    else:
        lexer.unpop_token(tok)
        return tuple()