# Questions tagged [recursion]

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### Verify maximal diameter of a tree in Dafny

I am trying to learn formal methods and have been learning Dafny and practicing by verifying Leetcode problems. I have gotten stuck on this one. https://leetcode.com/problems/diameter-of-binary-tree/...
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### Is there a multiway system which is equivalent to taking ZFC as axioms?

My understanding is that Stephen Wolfram's concept of a multiway system begins with certain rules and then generates all possible combinations of those rules. There are many distinct mathematical ...
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### Defining a Recursive Function decreasing on one argument with < and another structurally

I want to define a function which decreases in one argument using < and on another structurally. What is the least painful way to do this? Among the many options (Function, Program Fixpoint, ...
I am trying to formalise in Lean3 the notion of sum of squares in a ring. If $A$ is a ring, $n$ is an integer and $f$ is a function from  F_n:= \{ i \in \...