event/christies_24477_16/1 matches the site

public static Activity Auction_Of_Lot()
{
    var auctionOfLot = new Activity()
        .WithContext()
        .WithId("https://linked.art/example/event/christies_24477_16/1")
        .WithLabel("Auction of Lot 16")
        .WithClassifiedAs(Aat.Term("300420001", "Auction of Lot"));

    auctionOfLot.IdentifiedBy = [new Name("Auction of Lot 16").AsPrimaryName()];

    auctionOfLot.UsedSpecificObject = [
        new Set()
            .WithId("https://linked.art/example/set/24477_16_objects")
            .WithLabel("Lot 16")
    ];

    auctionOfLot.PartOf = [
        new Activity().WithId("https://linked.art/example/event/christies_24477")
    ];

    return auctionOfLot;
}

• Role shortcuts AsPrimaryName, AsAccessionNumber and AsSystemAssignedNumber each add a single classification, with the AAT terms Primary Name, Accession Number and System Number.
• Terms outside the registry The vocabulary registry holds only the terms linked.art itself publishes, so a dataset's own concepts, places and people are written with Aat.Term, Tgn.Place and Ulan.Person, giving the id and the label.

var activity = new Activity
{
    Context = ["https://linked.art/ns/v1/linked-art.json"],
    Id = "https://linked.art/example/event/christies_24477_16/1",
    Label = "Auction of Lot 16",
    ClassifiedAs = [Aat.Term("300420001", "Auction of Lot")],
    IdentifiedBy =
    [
        new Name("Auction of Lot 16")
        {
            ClassifiedAs = [Aat.PrimaryName],
        },
    ],
    UsedSpecificObject =
    [
        new Set
        {
            Id = "https://linked.art/example/set/24477_16_objects",
            Label = "Lot 16",
        },
    ],
    PartOf =
    [
        new Activity
        {
            Id = "https://linked.art/example/event/christies_24477",
        },
    ],
};

Generated from the object the example builds: every property that is set, as object initialisers, with the vocabulary constants where a term is in the registry. The fluent helpers are a convenience, not a requirement; this form and the one as written produce the same JSON.