Prove oscillatory leading-principal interlacing - #430

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/cache@5a3ec84eff668545956fd18022155c47e93e2684, actions/deploy-pages@d6db90164ac5ed86f2b6aed7e0febac5b3c0c03e, actions/upload-artifact@v4. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/