Almost Everywhere Convergence of Walsh Series of $L^2$ functions

I am currently reading the Hunt's papar (http://www.mathunion.org/ICM/ICM1970.2/Main/icm1970.2.0655.0662.ocr.pdf), and am wondering if there is any notes which presents his argument more comprehensively.

Thank you.

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5. This article of Gosselin ("On the convergence of Walsh-Fourier series for $L^2(0,1)$).
6. Billard's original article (in French) "Sur la convergence presque partout des séries de Fourier-Walsh des fonctions de l'espace $L^2(0,1)$"