def is_indvar(expr):
    assert isinstance(expr, string_types), "%s is not a string" % expr
    return re.match(r'^[a-df-z]\d*$', expr) is not None
Retrieves and displays a list of documents based on the user's choice.
dataset/ETHPy150Open nltk/nltk/nltk/sem/logic.py/is_indvar--crossover with--dataset/ETHPy150Open kuri65536/python-for-android/python-build/python-libs/gdata/samples/docs/docs_example.py/DocsSample._ListDocuments