  Using Chebyshev polynomials, C. Frohman and R. Gelca introduce a basis of the
Kauffman bracket skein module of the torus. This basis is especially useful
because the Jones-Kauffman product can be described via a very simple
Product-to-Sum formula. Presented in this work is a diagrammatic proof of this
formula, which emphasizes and demystifies the role played by Chebyshev
polynomials.
