A Dumb Introduction to Z3 (2025)

asibahi•41 minutes ago

Previously: https://news.ycombinator.com/item?id=45248558. Switched domains since then.

Surac•about 1 hour ago

Problems solved nothing learned. Poking my problems into a black box and getting numbers let me only learn how to poke numbers into black boxes

Arainach•about 1 hour ago

You learn how to use tools to solve problems and what kind of problems those tools can solve.

Using a database or 3D Printer isn't bad because you don't learn anything about the internals.

amelius•about 1 hour ago

It's still better than using AI, where even the authors of the black box don't really know what they're doing.

NooneAtAll3•about 1 hour ago

to be fair that's the general experience with such solvers

step 1: insert the problem

step 2: ???

step 3: profit

wren6991•about 3 hours ago

Z3 struggles with larger problems. CVC5 or Bitwuzla do a lot better once you get into anything complex.

If you're familiar with the Z3 Python API, you'll find the CVC5 one familiar.

Caveat: I mostly do logic design, maybe there are some software verification tasks where Z3 comes out ahead. I've never seen one though.

neel_k•about 1 hour ago

I do software verification. In my experience, Z3 is consistently but noticeably better than CVC5 at the kinds of problems we generate, though the two tools are close enough that you definitely want to architect your verification tool to be able to use either one (or both at once, in case you hit a problem which is pathological in one but not the other).

One place where Z3 exposes a superior interface to CVC5 is when you want to do term simplification. CVC5 does not have any real analogue to Z3's simplification tactics (like ctx-solver-simplify), so if you want to take a term and simplify it with respect to a set of assumptions, Z3 is your only choice. I think CVC5 has all the machinery you need to implement that stuff inside of it, but as a user you can't access it.

The place where CVC5 really pulls ahead of Z3 is when you want to produce proofs (eg, to integrate SMT solving into a proof assistant like Lean, HOL, or Rocq). Both tools have support for generating proofs, but CVC5's are noticeably less buggy, to the point that Lean's SMT integration uses CVC5, even though Leo de Moura (Lean's designer) was also the original designer of Z3.

jebarker•about 1 hour ago

I wonder how often interviewers object to the approach of solving their dynamic programming problem using a constraint solver?

inerte•5 minutes ago

Like any interview, randomly. Some of them will think it's amazing, clever person, chose the best tool for the job. Other will think it's weird, person is too clever, chose the worst tool for the job.

It totally depends for WHAT you're interviewing, but unlikely the company will want Z3-backed code, so most reactions would be the later.

amelius•about 3 hours ago

If the tutorial uses Rust, why didn't they use a solver written in Rust? Z3 was written in C++.

suddenlybananas•about 3 hours ago

What solver would you have them use? Z3 is very mature and the Rust bindings are pretty good in my (limited) experience.

amelius•about 3 hours ago

I would write the tutorial in C++, for a more direct experience.

Arainach•about 1 hour ago

There's nothing "more direct" - the different APIs for different languages call into the same underlying library, and most of them are more accessible and easier to work with than C++.

Z3 is presumably written in C++ for performance, but without data I am very confident the vast majority of programs that use Z3 consume it via one of the other APIs.

volemo•about 2 hours ago

I personally like to avoid the “writing in C++” experience. :/

suddenlybananas•about 2 hours ago

The author might not know C++ and you don't need to use C++ to effectively use z3.

A Dumb Introduction to Z3 (2025)

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