Thank you. So am I correct that he had created a type (for lack of a better term) representing a number of pushes and pops. And the monoid is the algebraic cons

Thank you. So am I correct that he had created a type (for lack of a better term) representing a number of pushes and pops. And the monoid is the algebraic construct that let's us combine those types. So faced with a string of square braces representing pushes and pops like in the example, we can divide them into chunks, count push and pops (also recording indices?) in parallel, and then combine them?