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sav07_lecture_3 [2007/03/22 13:44] yuanjianwz |
sav07_lecture_3 [2007/03/22 16:20] yuanjianwz |
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| We can apply these rules to reduce the size of formulas. | We can apply these rules to reduce the size of formulas. | ||
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| ==== Approximation ==== | ==== Approximation ==== | ||
| - | If (F -> G) is value, we say that F is stronger than F and we say G is weaker than F. | + | If (F -> G) is valid, we say that F is stronger than F and we say G is weaker than F. |
| When a formula would be too complicated, we can instead create a simpler approximate formula. To be sound, if our goal is to prove a property, we need to generate a *larger* relation, which corresponds to a weaker formula describing a relation, and a stronger verification condition. (If we were trying to identify counterexamples, we would do the opposite). | When a formula would be too complicated, we can instead create a simpler approximate formula. To be sound, if our goal is to prove a property, we need to generate a *larger* relation, which corresponds to a weaker formula describing a relation, and a stronger verification condition. (If we were trying to identify counterexamples, we would do the opposite). | ||