public override bool Equals(object obj)
        {
            SortedSetEqualityComparer <T> comparer = obj as SortedSetEqualityComparer <T>;

            if (comparer == null)
            {
                return(false);
            }
            return(this.comparer == comparer.comparer);
        }
        // Equals method for the comparer itself.
        public override bool Equals([NotNullWhen(true)] object?obj)
        {
            SortedSetEqualityComparer <T>?comparer = obj as SortedSetEqualityComparer <T>;

            return(comparer != null && _comparer == comparer._comparer);
        }