tests/rdb.sx shows the library as a small Datalog engine over fact
tables. Each table is an SX list of tuples, wrapped by a relation that
does (membero (list ...) table). Queries compose selection, projection,
and joins entirely in run* / fresh / conde / membero / intarith / nafc.
Five queries: dept filter, salary > threshold, employee-project join,
intersection (engineers on a specific project), anyone on multiple
distinct projects.
5 new tests, 336/336 cumulative.