object/spring/13 matches the site

public static HumanMadeObject Spring_in_Set()
{
    var spring = new HumanMadeObject()
        .WithContext()
        .WithId("https://linked.art/example/object/spring/13")
        .WithLabel("Jeanne (Spring) by Manet")
        .WithClassifiedAs(Aat.Painting, Aat.TypeOfWork);

    spring.IdentifiedBy = [new Name("Jeanne (Spring)")];

    spring.MemberOf = [
        new Set()
            .WithId("https://linked.art/example/set/exhset")
    ];

    return spring;
}

• Metatype classification The second argument classifies the first, not the object: WithClassifiedAs(Aat.Description, Aat.Statement) says this is a Description, and Description is a kind of Statement. The Plain C# form shows the nesting.

var humanMadeObject = new HumanMadeObject
{
    Context = ["https://linked.art/ns/v1/linked-art.json"],
    Id = "https://linked.art/example/object/spring/13",
    Label = "Jeanne (Spring) by Manet",
    ClassifiedAs =
    [
        new Type("http://vocab.getty.edu/aat/300033618", "Painting")
        {
            ClassifiedAs = [Aat.TypeOfWork],
        },
    ],
    IdentifiedBy = [new Name("Jeanne (Spring)")],
    MemberOf =
    [
        new Set
        {
            Id = "https://linked.art/example/set/exhset",
        },
    ],
};

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.