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14 lines
1.3 KiB
14 lines
1.3 KiB
\begin{itemize}
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\item \textbf{Start a proof.} At the top of your page write the premises, at the bottom write the conclusion.
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\item \textbf{Work in both directions to fill the gap.} Work from the top to the bottom
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by working with the premises, and simultaneously work upwards by using the conclusion.
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\item \textbf{Look at the conclusion first.} If the conclusion is of the form $\varphi \rightarrow \psi$, then immediately apply $\impi$.
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You still have to fill the gap in the box, but you have an extra assumption to work with and a simpler conclusion you try to reach. Similar, if your conclusion is of fhe form $\neg \varphi$, apply $\negi$ to make your life easier.
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\item \textbf{Assumption boxes.} At any time you can introduce a formula as assumption, by choosing a proof rule that opens the box.
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The box defines the scope of the assumption. By opening a box you introduce an assumption.
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But don't forget, you have to close the box precisely as
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defined by the applied proof rule.
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\item \textbf{What rule should you apply?} The rules $\impi$ and $\negi$ make your life easier, apply them whenever you can.
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There is no easy recipe for when to use the other rules. The best way to get the hang of it is doing many proofs
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by yourself.
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\end{itemize}
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