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sav07_lecture_3_skeleton [2007/03/20 14:27] vkuncak |
sav07_lecture_3_skeleton [2007/03/20 14:27] vkuncak |
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| * efficient | * efficient | ||
| * create formulas that we can prove later | * create formulas that we can prove later | ||
| + | |||
| ==== Formulas for basic statements ==== | ==== Formulas for basic statements ==== | ||
| Line 23: | Line 24: | ||
| R(x=t) = (x=t & y=y_0 & error=error_0) | R(x=t) = (x=t & y=y_0 & error=error_0) | ||
| - | <b>Note</b>: all our statements will have the property that if error_0 = true, then error=true. That is, you can never recover from an error state. This is convenient: if we prove no errors at the end, then there were never errors in between. | + | ***Note***: all our statements will have the property that if error_0 = true, then error=true. That is, you can never recover from an error state. This is convenient: if we prove no errors at the end, then there were never errors in between. |
| - | <b>Note</b>: the condition y=y_0 & error=error_0 is called <b>frame condition</b>. There are as many conjuncts as there are components of the state. This can be annoying to write, so let us use shorthand frame(x) for it. The shorthand frame(x) denotes a conjunction of v=v_0 for all v that are distinct from x (in this case y and error). We can have zero or more variables as arguments of frame, so frame() means that nothing changes. | + | ***Note***: the condition y=y_0 & error=error_0 is called <b>frame condition</b>. There are as many conjuncts as there are components of the state. This can be annoying to write, so let us use shorthand frame(x) for it. The shorthand frame(x) denotes a conjunction of v=v_0 for all v that are distinct from x (in this case y and error). We can have zero or more variables as arguments of frame, so frame() means that nothing changes. |
| R(havoc x) = frame(x) | R(havoc x) = frame(x) | ||