concept/exhidea/1 matches the site

public static PropositionalObject Exhibition_Concept()
{
    var concept = new PropositionalObject()
        .WithContext()
        .WithId("https://linked.art/example/concept/exhidea/1")
        .WithLabel("Idea for Manet and Modern Beauty")
        .WithClassifiedAs(Aat.Exhibition);

    concept.IdentifiedBy = [new Name("Manet and Modern Beauty").AsPrimaryName()];

    concept.About = [
        Aat.Term("300055821", "Beauty"),
        Ulan.Person("500010363", "Manet")
    ];

    concept.CreatedBy = new Creation()
    {
        CarriedOutBy = [
            new Person()
                .WithId("https://linked.art/example/person/allan")
                .WithLabel("Scott Allan"),
            new Person()
                .WithId("https://linked.art/example/person/beeny")
                .WithLabel("Emily Beeny"),
            new Person()
                .WithId("https://linked.art/example/person/groom")
                .WithLabel("Gloria Groom"),
        ]
    };

    return concept;
}

• 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 propositionalObject = new PropositionalObject
{
    Context = ["https://linked.art/ns/v1/linked-art.json"],
    Id = "https://linked.art/example/concept/exhidea/1",
    Label = "Idea for Manet and Modern Beauty",
    ClassifiedAs = [Aat.Exhibition],
    IdentifiedBy =
    [
        new Name("Manet and Modern Beauty")
        {
            ClassifiedAs = [Aat.PrimaryName],
        },
    ],
    CreatedBy = new Creation
    {
        CarriedOutBy =
        [
            new Person
            {
                Id = "https://linked.art/example/person/allan",
                Label = "Scott Allan",
            },
            new Person
            {
                Id = "https://linked.art/example/person/beeny",
                Label = "Emily Beeny",
            },
            new Person
            {
                Id = "https://linked.art/example/person/groom",
                Label = "Gloria Groom",
            },
        ],
    },
    About = [Aat.Term("300055821", "Beauty"), Ulan.Person("500010363", "Manet")],
};

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.