j-pb

    // The entity! macro returns a rooted fragment; merge its facts into
    // a TribleSet via `+=`.
    let herbert = ufoid();
    let dune = ufoid();
    let mut library = TribleSet::new();

    library += entity! { &herbert @
        literature::firstname: "Frank",
        literature::lastname: "Herbert",
    };

    library += entity! { &dune @
        literature::title: "Dune",
        literature::author: &herbert,
        literature::quote: ws.put(
            "I must not fear. Fear is the mind-killer."
        ),
    };

    ws.commit(library, "import dune");

    // `checkout(..)` returns a Checkout — a TribleSet paired with the
    // commits that produced it, usable for incremental delta queries.
    let catalog = ws.checkout(..)?;
    let title = "Dune";

    // Multi-entity join: find quotes by authors of a given title.
    // `_?author` is a pattern-local variable that joins without projecting.
    for (f, l, quote) in find!(
        (first: String, last: String, quote),
        pattern!(&catalog, [
            { _?author @
                literature::firstname: ?first,
                literature::lastname: ?last
            },
            { _?book @
                literature::title: title,
                literature::author: _?author,
                literature::quote: ?quote
            }
        ])
    ) {
        let quote: View<str> = ws.get(quote)?;
        let quote = quote.as_ref();
        println!("'{quote}'\n - from {title} by {f} {l}.");
    }