[systoll]

I don't disbelieve you but… where?

I don't think I’ve ever heard it used like that, and in trying to find any example other than the page we’re commenting on, I’ve only found counterexamples.

Whether it’s wikipedia’s 'Glossary of Chess Problems' or OzProblems or 'Sam Loyd and his chess problems' from 1913, they’re all using 'legal' as synonymous with 'reachable'.