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

Pattern<TSource1, TSource2, TSource3>

public class Pattern<TSource1, TSource2, TSource3> : Pattern
Represents a join pattern over three observable sequences.
public Pattern<TSource1, TSource2, TSource3, TSource4> And<TSource4>(IObservable<TSource4> other)

Creates a pattern that matches when all four observable sequences have an available element.

public Plan<TResult> Then<TResult>(Func<TSource1, TSource2, TSource3, TResult> selector)

Matches when all observable sequences have an available element and projects the elements by invoking the selector function.