I came across the following paragragh in the paper entitled "simulation of Power-Law Relaxations by Analog circuits: Fractal Distribution of Relaxation Times and Non-integer Exponents"
In linear system, a function f(x) can be expressed by a superposition of a suitable function h(x) as: $$ f(t)=\int_0^\infty g(\tau)h(\tau,t)d\tau $$ where g(t) is a distribution function.
would you please suggest further reading on this point?