References
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- B. Ebanks, A Levi-Civita equation on monoids, two ways, Ann. Math. Sil. 36 (2022), no. 2, 151–166.
- B. Ebanks, A new cosine functional equation, Aequationes Math. 99 (2025), no. 6, 2713–2723.
- H. Stetkær, Functional Equations on Groups, World Scientific Publishing, Singapore, 2013.
- H. Stetkær, The sine addition law applied to a cosine equation. (private communication)