<PackageReference Include="System.Reactive" Version="6.0.0" />

System.Reactive.Joins.Pattern<TSource1, TSource2>

public class Pattern<TSource1, TSource2> : Pattern
namespace System.Reactive.Joins { public class Pattern<TSource1, TSource2> : Pattern { public Pattern<TSource1, TSource2, TSource3> And<TSource3>(IObservable<TSource3> other); public Plan<TResult> Then<TResult>(Func<TSource1, TSource2, TResult> selector); } }