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Skip a subgoal while proving in Isabelle

proof,isabelle,theorem-proving,isar
I am trying to prove a theorem but got stuck at a subgoal (that I prefer to skip and prove later). How can I skip this and prove the others ? First, I tried oops and sorry but they both abort the entire proof (instead of the only subgoal). I...

Create a quotient-lifted type with polymorphism over working set and equivalence relation in Isabelle/HOL

set,higher-order-functions,isabelle,theorem-proving,isar
I would like to create a quotient type with quotient_type in Isabelle/HOL in which I would left "non-constructed" the non-empty set S and the equivalence relation ≡. The goal is for me to derive generic properties w.r.t. S and ≡ over the quotient-lifted set S/≡. In this way, it would...

Proof assistant for mathematics only

proof,agda,idris,proof-of-correctness,isar
Most proof assistants are functional programming languages with dependent types. They can proof programs/algorithms. I'm interested, instead, in proof assistant suitable best for mathematics and only (calculus for instance). Can you recommend one? I heard about Mizar but I don’t like that the source code is closed, but if it...

Proving a simple arithmetic statement with rewriting in Isabelle

isabelle,isar
I am trying to prove a big case distinction in Isabelle for some (conceptually) simple arithmetic statement. During the proof, I stumbled upon the following subgoal. ⋀d l k. 0 < d ⟹ ¬ 2 * k + 1 ≤ 2 * l ⟹ 2 * l ≠ 1 ⟹...