Jan Burse, erstellt 03. Okt 2016
* Prolog code for the database query benchmark.
* This is the benchmark of page 226 of:
* Warren, D.H.D. (1983): Applied Logic - Its Use and
* Implementation as a Programming Tool,
* Technical Note 290, SRI International, 1983
* We use integer division instead of float division,
* since float division is not yet available in Jekejeke
* Prolog 0.8.4. Further complication by two temporary
* variables T1 and T2.
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% density(-Atom, -Integer)