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The standard indexing method is only useful for procedures with a
database-like structure, i.e. the first argument is a key (or at least
a quasi-key: practically all constants are different, there a hardly
p(c1, ...) :- ... .
p(c2, ...) :- ... .
p(cn, ...) :- ... .
Thus the standard indexing method does not work in the following cases:
- the quasi-key is not the first argument of the procedure
- the procedure can be split into several blocks each having another
argument as a quasi-key
- the quasi-key is spread over several arguments
- there is more than one argument (group) that could serve as a quasi-key
(this is important if the argument that is best suited for indexing
is rarely instantiated in calls)
- some combinations of cases 1-3 with case 4