- Riemann zeta function (Wikipedia)
The Riemann zeta function or Euler–Riemann zeta function, denoted by the Greek letter ζ (zeta), is a mathematical function of a complex variable
- Rhyacian (Wikipedia)
The Rhyacian Period ( /raɪˈeɪsi.ən/; Ancient Greek: ῥύαξ, romanized: rhýax, meaning “stream of lava”) is the second geologic period in the Paleoproterozoic Era and lasted from 2300 Mya to 2050 Mya (million years ago). Instead of being based on stratigraphy, these dates are defined chronometrically.