Datalog query with leapjoin

Hey, I'm just playing around with datafrog and trying to translate some basic datalog queries to the equivalent Rust code. I am wondering what something like the following snippet looks like in datafrog?

node(1, 'A').
node(2, 'B').
node(3, 'C').
node(4, 'D').

edge(1, 2).
edge(2, 3).
edge(3, 1).
edge(1, 4).

depthTwo(W1, W2) :-
    page(T1, W1),
    page(T2, W2),
    link(T1, T2).

I'm mostly interested in leapjoin and have tried something like:

let mut iteration = Iteration::new();

let pages: Relation<_> = vec![
    (1, "super.com"),
    (2, "page.com"),
    (3, "subpage.com"),
    (4, "minpage.com"),
]
.into();
let edges: Relation<(u32, u32)> = vec![(1, 2), (2, 3), (3, 1), (1, 4)].into();
let edges_rev: Relation<_> = edges.iter().map(|&(from, to)| (to, from)).collect();

let var = iteration.variable::<(u32, &str)>("var");
var.insert(pages.clone());

while iteration.changed() {
    var.from_leapjoin(
        &var,
        // So I technically would like to filter by the edges
        // but the nodes i want to filter by are not really there yet?
        // And I can't extend with nodes and filter with the edges
        edges_rev.extend_with(|&(a, _)| a),
        //
        |&(a, b), &c| (a, b),
    );
}

But I can't quite wrap my head around how the leapers work even after reading the comment given in the source code of the repo. Any pointers would be appreciated!

Start with the Iteration, Variable, and from_leapjoin entry points shown in the issue, then read the leaper comments in the source code. Compare the supplied pages and edges relations with the documented leapjoin inputs; done means a clear Rust equivalent or usage explanation for the Datalog query.