calc PI https://en.wikipedia.org/wiki/Pi code https://github.com/HHS-IntroProgramming/Calculate-Pi https://github.com/morphx666/CalcPi https://github.com/Drethic/eve-pi-calc https://github.com/SaltyPaws/calculator_pi https://github.com/nohal/Calc_pi_muparser https://github.com/coq-contribs/pi-calc