fugacity coefficient, Math - title

https://dx.doi.org/10.1351/goldbook.F02544
Ratio of fugacity to the partial pressure of a gaseous constituent.
Source:
PAC, 1994, 66, 533 (Standard quantities in chemical thermodynamics. Fugacities, activities and equilibrium constants for pure and mixed phases (IUPAC Recommendations 1994)) on page 539