<unk> , stated by Josiah Willard<unk>  in the 1870s, is the fundamental rule on which<unk>  diagrams are based.
where π ( or in some references P ) is the number of<unk> s present in equilibrium (Types of solid, liquid, gas<unk> s etc), N=number of non computational variables.
F is the number of degrees of freedom or independent variables taken from temperature, pressure and composition of the<unk> s present.
C is the number of chemical components required to describe the system
Gibbs' phase rule
Hund's rule of maximum multiplicity
Naegele's rule
Chichibabin reaction
The U Wave
Heterolysis
Osborn wave
Wolffenstein-Böters reaction