using System;
using System.Text.RegularExpressions;

public class Test
{
	public static void Main()
	{
		var isMatch1 = new Regex(@"[^a]*|[^a]*a[^b]*").IsMatch("ab");
		Console.WriteLine("[ab] {0}", isMatch1);
		var isMatch2 = new Regex(@"[^a]*|[^a]*a[^b]*|[^a]*a[^b]*b[^c]*").IsMatch("abc");
		Console.WriteLine("[abc] {0}", isMatch2);
	}
}