\[
\newcommand{\tr}{\Rightarrow}
\newcommand{\trs}{\tr^{\!\ast}}
\newcommand{\rlnm}[1]{\mathsf{(#1)}}
\newcommand{\rred}[1]{\xrightarrow{#1}}
\newcommand{\rreds}[1]{\mathrel{\xrightarrow{#1}\!\!^*}}
\newcommand{\cl}{\mathsf{Cl}}
\newcommand{\pow}{\mathcal{P}}
\newcommand{\matches}{\mathrel{\mathsf{matches}}}
\newcommand{\kw}[1]{\mathsf{#1}}
\]
Left association example
\[\begin{array}{l|l}
\text{when we write...} & \text{we mean the tree...} \\\hline
5 - 4 + 1 & (5 - 4) + 1 \\
1 + 3 - 6 & (1 + 3) - 6\\
6 * 7 * 8 & (6 * 7) * 8\\
1 + 1 + 2 & (1 + 1) + 2\\
8 - 4 - 1 & (8 - 4) - 1
\end{array}\]