In which namespace are these extension methods: AsFunctions, AsCalls? .net 4.6.2?

[gunpal5]

using var client = new HttpClient();
var model = new Gpt35TurboModel(apiKey, client);

var service = new WeatherService();
model.AddGlobalFunctions(service.AsFunctions(), service.AsCalls());

var response = await model.GenerateAsync(new ChatRequest(
Messages: new []
{
"You are a helpful weather assistant.".AsSystemMessage(),
"What's the weather like today?".AsHumanMessage(),
"Sure! Could you please provide me with your location?".AsAiMessage(),
"Dubai, UAE".AsHumanMessage(),
}));

Console.WriteLine(response.Messages.AsHistory());

I can't find Methods AsFunctions, AsCalls, AsSystemMessage, AsHumanMessage etc. I am trying to use it in .Net 4.6.2