Criteria for evaluating errata changes for EXISTS

[afs]

This issue is to collect criteria we can use to assess the different proposals for EXISTS.

https://github.com/w3c/sparql-query/issues?q=is%3Aissue+is%3Aopen+exists

SPARQL Tests:
SPARQL 1.1 test suite - exists
SPARQL 1.1 test suite - negation

TPAC 2023 Slides:
SPARQL @ TPAC 2023.pdf

[afs]

Criterion: continuity

SPARQL 1.1 queries that do not involve the identified problem areas should not be affected.

[Tpt]

Criterion: provide interesting features

The MINUS operator already exists with anti-join semantic. It would be nice for FILTER NOT EXISTS to not be a duplicate of MINUS by not making it have the exact same semantic as MINUS.