As a programming analogy: imagine mathematics is a big codebase and "prime" is a commonly-used function defined within that codebase. You could refactor "prime

As a programming analogy: imagine mathematics is a big codebase and "prime" is a commonly-used function defined within that codebase. You could refactor "prime" to allow 1, provided you refactor all the call sites to work with that new definition too. Consensus seems to be that this refactoring would add LOC and reduce code readability, probably leading to someone submitting a patch soon after with a "prime-but-not-one" function and using that everywhere.