What is your current code that results in that error?

For reference, see how the implementation is required in the test namespace (I assume their tests run just fine, I haven't actually checked): https://github.com/originrose/aljabr/blob/master/test/thinktopic/aljabr/test_all.cljc#L3-L6

Currently requiring and calling it like this, still getting the above error.

The error goes away if I take out the test-mat bit. using shadow.cljs if thats relevant?

Shadow-cljs shouldn't be relevant here. But that test NS is incomplete in the sense that it only uses mat/shape from the whole core.matrix API.

Try using (mat/matrix :aljabr [...]). Does it work?

mat/matrix works without the keyword, the issue is seemingly only when I call mat/inverse on something.

or, on a matrix, specifically

But does adding that keyword fix the error? Regardless of what expression resulted in the error.

Adding the keyword to mat/inverse before the matrix throws an error, too many arguments

You need to add it to the matrix call.

Even if it's the inverse call that causes that error.

I tried this (mat/inverse (mat/matrix :aljabr [[1 2][3 4]])) and got this error INFO: No dynamic loading of implementations in Clojurescript. You must require an implementation explicitly in a namespace, for example thinktopic.aljabr.core.

Is the only symptom just that error message? Or do things not work at all?

Instead of explicitly providing that keyword every time, you can also do (mat/set-current-implementation :aljabr), just like here: https://github.com/mikera/core.matrix/blob/develop/src/test/cljs/clojure/core/matrix/test_basics.cljs#LL19C41-L19C41 Judging by the implementation, it will still result in that error. But it's a false symptom because the error is printed unconditionally.