using System;
using System.Linq;
using System.Text.RegularExpressions;

public class Test
{
	public static void Main()
	{
		var delim = new string[] {"fox", "lazy"};
		var delimGroup = "(?:"+string.Join("|", delim.Select(Regex.Escape))+")";
		var pattern =  @"\s(?="+delimGroup+")|(?<="+delimGroup+@")\s";
		var x = Regex.Split(
			"quick brown fox jumps over the lazy dog"
	    ,   pattern
	    );
	    Console.WriteLine(pattern);
	    foreach (var s in x)
	        Console.WriteLine("[{0}]", s);
	}
}