5.2.1.0.3 Declarations for Call Variance and Call Subsumption

By default tabled predicate use call variance. However, subsumption-based tabling can be made the default by giving XSB the -S option at invocation (refer to Section 3.7). More versatile constructs are provided by XSB so that the tabling method can be selected on a per predicate basis. Use of either directive use_variant_tabling/1 or use_subsumptive_tabling/1, described in Section 6.14.1, ensures that a tabled predicate is evaluated using the desired strategy regardless of the default tabling strategy.