In general, a process function X may be either holonomic or non-holonomic. For a holonomic process function, an auxiliary state function (or integrating factor) λ may be defined such that Y = λX is a state function. For a non-holonomic process function, no such function may be defined. In other words, for a holonomic process function, λ may be defined such that dY = λδX is an exact differential. For example, thermodynamic work is a holonomic process function since the integrating factor λ = ⁠ 1 / p ⁠ (where p is pressure) will yield exact differential of the volume state function dV = ⁠ δW / p ⁠. The second law of thermodynamics as stated by Carathéodory essentially amounts to the statement that heat is a holonomic process function since the integrating factor λ = ⁠ 1 / T ⁠ (where T is temperature) will yield the exact differential of an entropy state function dS = ⁠ δQ / T ⁠.