Please see this link to properly format your code in the discourse. Anyway, you're logging too much to the console, that's the reason for the error. If you get rid of your console.log statements, it should work.

Hello. Sorry for taking so long to respond. I've only read one book about the functional approach - the Structure and interpretation of computer programs. You can find it using the keywords MIT 6.001.

@maks88sgt would you recommend any particular book regarding functional programming? Thanks.

You don't specify what went wrong. Which test case did you fail on, and what output did you see from that failure?
(If it's a stack trace, the first 1-2 lines are enough).

thank you for your solution :)

Thanks for your feedback. I recommend reading something about functional programming. This greatly affects your coding style and allows you to think a little differently than usual.

No, I meant you can, your code is not complete, you only used + more than one time, what about *? Check the examples in the description.

No, read this again:

You can use the same operation more than once.

And next time mark your post as having spoiler content.