I want to know the answer to the following question:
What has been the result of attempts to connect Sumerian to other language groups?
All the background I'm provided with is that "Some authors have proposed that there may be evidence of a sub-stratum or add-stratum language for geographic features and various crafts and agricultural activities, called variously Proto-Euphratean or Proto Tigrean, but this is disputed by others.". Is that enough to answer the question?