Let $M = (\mathbb{R}^n, \mathcal{L}, \mu)$ be a D1744: Lebesgue measure space.
Let $\mathfrak{L}^1 = \mathfrak{L}^1(M)$ be the D2401: Set of absolutely integrable functions on $M$.

Then \begin{equation} \forall \, f, g, h \in \mathfrak{L}^1 : (f * g) * h = f * (g * h) \end{equation}