"Example of Optional and Params Lambda Arguments"

var multiplierFunc = (string input, int numMultiples = 2) => String.Join(null, Enumerable.Repeat(input, numMultiples));
Console.WriteLine(multiplierFunc("hello")); // "hellohello"

var joinFunc = (params string[] input) => String.Join(null, input);
Console.WriteLine(joinFunc("hi", " ", "there")); // "hi there"