System.Func<T1, T2, T3, TResult>
namespace System
{
public delegate TResult Func<in T1, in T2, in T3, in T4, in T5, in T6, out TResult> (T1 arg1, T2 arg2, T3 arg3, T4 arg4, T5 arg5, T6 arg6);
}
namespace System
{
public delegate TResult Func<in T1, in T2, in T3, out TResult> (T1 arg1, T2 arg2, T3 arg3);
}