EDGEMAP is a higher function that takes in two functions, in this case, UPDATE and COND, where COND serves as a predicate, and UPDATE is the action that would be carried out when the predicate defined by COND is met.

It's very cool that Ligra is able to do so much with such a simple primitive. Edgemap is something you can implement in many languages with basic functional features reasonably easily. I imagine that a Rust port of it could be a reasonably tiny library.

A student noted in the chat that we can think of this as a map-filter operation, where we define maps over vertices and edges, and filter by certain conditions (whether or not COND(j) is true, etc.)