Duffy transformation for singular integration

Hello! Thanks for the great project! I have a question about singular and hypersingular integration for the Laplace kernel.

As far as I understand, the BEMPP uses the Duffy transformation for integration. Could you please tell me if there is a scientific paper with a detalied description of this method?

Finally, I found the description of the method. Details are given in the book Sauter, S. A., Schwab, C., Sauter, S. A., & Schwab, C. (2011). Boundary element methods, paragraph 5.2.4