using System;
using System.Text.RegularExpressions;
 
public class Test
{
	public static void Main()
	{
		string testcase0 = @"fun(abc) fun3()";
		string testcase1 = @"fun(\\\)\)) fun3()";
		string testcase2 = @"fun(fun2(\)\\\() ) fun3()";
 
		Regex catchRegex = new Regex(@"^fun\(((?:[^()\\]|\\.|(?<o>\()|(?<-o>\)))+(?(o)(?!)))\)(.*$)");
 
		Console.WriteLine(catchRegex.Match(testcase0).Groups[1]); // 'abc'
		Console.WriteLine(catchRegex.Match(testcase0).Groups[2]); // ' fun3()'
 
		Console.WriteLine(catchRegex.Match(testcase1).Groups[1]); // '\\\)\)'
		Console.WriteLine(catchRegex.Match(testcase1).Groups[2]); // ' fun3()'
 
		Console.WriteLine(catchRegex.Match(testcase2).Groups[1]); // 'fun2(\)\\\()'
		Console.WriteLine(catchRegex.Match(testcase2).Groups[2]); // ' fun3()'
	}
}

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