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Artificial Intelligence and Soft Computing: Behavioral ... - Arteimi.info

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The second rule is generally called weak negation, which is in contrast to the<br />

following rule, called strong negation.<br />

∀t , ( t1 ≤t) ∧ (t2 ≥ t) ∧ Holds(t1, t2, ¬ φ) ¬ Holds(t, φ) .<br />

The weak <strong>and</strong> strong negation both support the following properties:<br />

For weak negation,<br />

├ Holds(t1, t2, ¬ ¬ q)<br />

├ ¬Holds(t1, t2, ¬ q)<br />

├ ¬¬Holds(t1, t2, q)<br />

├ Holds (t1, t2, q).<br />

For strong negation,<br />

├ ∀ t , ( t1 ≤ t) ∧ (t2 ≥ t) ∧ Holds(t1, t2, ¬ ¬p)<br />

├ ∀ t , ( t1 ≤ t) ∧ (t2 ≥ t) ∧ ¬ Holds(t1, t2, ¬p)<br />

├ ∀ t , ( t1 ≤t) ∧ (t2 ≥ t) ∧ ¬ ¬ Holds(t1, t2, p)<br />

├ ∀t , ( t1 ≤t) ∧ (t2 ≥ t) ∧ Holds(t1, t2, p).<br />

But there exists evidence of proving Holds(t1, t2, p) ∨ Holds(t1, t2, q) from<br />

Holds(t1, t2, p∨q), which is not feasible by strong negation [3].<br />

11.8 Reasoning with Both Space <strong>and</strong> Time<br />

We have discussed various schemes for reasoning with space <strong>and</strong> time<br />

independently. However, there exist circumstances, when both are required<br />

concurrently. A formalization of reasoning techniques in variation of both<br />

spatial <strong>and</strong> temporal events is an open area of research till date. We here just<br />

illustrate the justification of such reasoning with an example.<br />

Example 11.8: Suppose one summer evening, a hot burst of wind moving in<br />

the west causes a fire at the hill, which gradually started spreading in the<br />

village (Fig. 11.10). A villager reports to the fire brigade station at time t1. A<br />

fire brigade now has to plan the route, so that it can reach the village at the<br />

earliest. There are only two roads, one the hillside road (road1) that requires<br />

longer time of traversal <strong>and</strong> the other road (road2) which requires crossing a<br />

river through a bridge to reach the village. The pilot of the fire brigade car<br />

thinks that it can reach E1 end of the bridge within 15 minutes, but crossing<br />

the river after 15 minutes will be difficult, as by that time many villagers too<br />

will rush to cross it from other end E2 of the bridge. But traversal through the<br />

road1 will require 20 minutes more than the time required through road2 had

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