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Guarded logic is a choice set of dynamic logic involved in choices, where outcomes are limited. A simple example of guarded logic is as follows: if X is true, then Y, else Z can be expressed in dynamic logic as (X?;Y)∪(~X?;Z). This shows a guarded logical choice: if X holds, then X?;Y is equal to Y, and ~X?;Z is blocked, and a ∪block is also equal to Y. Hence, when X is true, the primary performer of the action can only take the Y branch, and when false the Z branch. A real-world example is the idea of paradox: something cannot be both true and false. A guarded logical choice is one where any change in true affects all decisions made down the line. ==History== Before the use of guarded logic there were two major terms used to interpret modal logic. Mathematical logic and database theory (Artificial Intelligence) were first-order predicate logic. Both terms found sub-classes of first-class logic and efficiently used in solvable languages which can be used for research. But neither could explain powerful fixed-point extensions to modal style logics. Later Moshe Y. Vardi made a conjecture that a tree model would work for many modal style logics. The guarded fragment of first-order logic was first introduced by Hajnal Andréka, István Németi and Johan Van Benthem in their article Modal languages and bounded fragments of predicate logic. They successfully transferred key properties of description, modal, and temporal logic to predicate logic. It was found that the robust decidability of guarded logic could be generalized with a tree model property. The tree model can also be a strong indication that guarded logic extends modal framework which retains the basics of modal logics. Modal logics are generally characterized by invariances under bisimulation. It also so happens that invariance under bisimulation is the root of tree model property which helps towards defining automata theory. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Guarded logic」の詳細全文を読む スポンサード リンク
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