# Questions tagged [isar]

Use this tag for the ISAR (Intelligible semi-automated reasoning) proof language in the Isabelle proof assistant.

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### What is an assumption in Isar?

I have the following code: lemma assumes "A" shows "A ∧ A" proof - show "A ∧ A" apply (rule conjI) apply assumption Now, ...
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1 vote
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### Result contains obtained parameters? So what?

When proving an existential claim, you can use rule exI and exhibit an example; this is a sufficient proof (as you'd expect!). Conversely, if you have an ...
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### Type class constaint is ignored in type synonym definition

My class constraint is ignored in a type synonym definition: for type_synonym 'value myTypeOperator = "'value::group_add" I get ...
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### Discharging an assumption in Isar

In Isar, one can make an assumption and then use it as a premise for an implication goal later. ...
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### Simple and proper methods in Isar

https://isabelle.systems/cookbook/src/proofs/methods/Chained_Facts.thy talks about We note a slight difference. In the variant with intro, a trivial goal remains that we need to solve by ‹assumption›....
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### Picking this and calculation in Isabelle/JEdit output

This is a follow-up to How to write a low-level proof in Isar? Having ...
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1 vote
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### How to write a low-level proof in Isar?

I would like to formalize ...
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### Is there an elegant way of proving an equality A=B by going in both directions?

I would like to prove an equality by splitting it into a proof in each direction. Is there a more elegant style to start such a proof than this way:: ...
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### Why is Isabelle usually not just Isabelle but Isabelle/<xyz>?

For most proof assistants the name alone is common, E.g. Coq, Lean but with Isabelle it is often seen as Isabelle/<xyz>? Why the two parts? What is Isabelle/HOL Isabelle/FOL Isabelle/ZF ...
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