namespace System.Collections.ObjectModel
{
    public class ReadOnlySet<T> : ICollection<T>, IEnumerable, IEnumerable<T>, IReadOnlyCollection<T>, IReadOnlySet<T>, ISet<T>, ICollection
    {
        public bool IsProperSupersetOf(IEnumerable<T>! other);
    }
}

An error has occurred. This application may no longer respond until reloaded. Reload 🗙