Keep Windows Forms Singleton via Mutex key word

using system;
using system.collections.generic;
using system.linq;
using system.threading;
using system.threading.tasks;
using system.windows.forms;

namespace windowsformsapplication3
{
    static class program
    {
        /// <summary>
        /// the main entry point for the application.
        /// </summary>
        [stathread]
        static void main()
        {
            application.enablevisualstyles();
            application.setcompatibletextrenderingdefault(false);
            const string appname = "windowsformsapplication3";
            bool creatednew;
            mutex mut = new mutex(true, appname, out creatednew);
            if (!creatednew)
            {
                messagebox.show($"windowsformsapplication3 is already running!", "multiple instances");
                return;
            }
            application.run(new form1());
        }
    }
}
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