Research paper. — Pallas: revue d’études antiques. — 2017. — № 103. — p. 15-23.
Dr. Stefan Höfler analyzes examples of “palma rule” – Proto-Indo-European *CR̥HC → Lat. CRāC is the usual result in Latin, but PIE.*pĺ̥h2-meh2 → Lat. palma, instead of expected †plāma.