System.Action<T1, T2, T3, T4, T5, T6, T7, T8, T9>

public sealed delegate Action<T1, T2, T3, T4, T5, T6, T7, T8, T9> : MulticastDelegate

namespace System { public delegate void Action<in T1, in T2> (T1 arg1, T2 arg2); }