An important characteristic of this code is its ability to cope with the various modes in which the predicates can be evoked : Any argument might be a variable, a ground term, or a partly instantiated term.
12.
Application of this rule can however be restricted by delaying the application of the rule until no other rule is applicable and by restricting the application of the rule to ground terms that already appear in the path of the tableau.
13.
Every sufficiently large ground term " t " in a recognizable tree language " L " can be vertically tripartited such that arbitrary repetition ( " pumping " ) of the middle part keeps the resulting term in " L ".
14.
Contrary to regular logic programming, this also requires a constraint to be satisfied : X > 0, the constraint in the body of the last clause ( in regular logic programming, X > 0 cannot be proved unless X is bound to a fully-ground term and execution of the program will fail if that is not the case ).
