System.Xml.Schema.NamespaceList.RemoveNamespace C# (CSharp) Method

        private void RemoveNamespace(string tns) {
            if (this.set[tns] != null) {
                this.set.Remove(tns);
            }
        }

        public static NamespaceList Intersection(NamespaceList o1, NamespaceList o2, bool v1Compat)
        {
            NamespaceList nslist = null;

            Debug.Assert(o1 != o2);      //clause 1
            if (o1.type == ListType.Any) //clause 2 - o1 is any
            {
                nslist = o2.Clone();
            }
            else if (o2.type == ListType.Any)   //clause 2 - o2 is any
            {
                nslist = o1.Clone();
            }
            else if (o1.type == ListType.Set && o2.type == ListType.Other)   //Clause 3 o2 is other
            {
                nslist = o1.Clone();
                nslist.RemoveNamespace(o2.targetNamespace);
                if (!v1Compat)
                {
                    nslist.RemoveNamespace(string.Empty); //remove ##local
                }
            }
            else if (o1.type == ListType.Other && o2.type == ListType.Set)   //Clause 3 o1 is other
            {
                nslist = o2.Clone();
                nslist.RemoveNamespace(o1.targetNamespace);
                if (!v1Compat)
                {
                    nslist.RemoveNamespace(string.Empty); //remove ##local
                }
            }
            else if (o1.type == ListType.Set && o2.type == ListType.Set)   //clause 4
            {
                nslist      = o1.Clone();
                nslist      = new NamespaceList();
                nslist.type = ListType.Set;
                nslist.set  = new Hashtable();
                foreach (string ns in o1.set.Keys)
                {
                    if (o2.set.Contains(ns))
                    {
                        nslist.set.Add(ns, ns);
                    }
                }
            }
            else if (o1.type == ListType.Other && o2.type == ListType.Other)
            {
                if (o1.targetNamespace == o2.targetNamespace)   //negation of same namespace name
                {
                    nslist = o1.Clone();
                    return(nslist);
                }
                if (!v1Compat)
                {
                    if (o1.targetNamespace == string.Empty)   // clause 6 - o1 is negation of absent
                    {
                        nslist = o2.Clone();
                    }
                    else if (o2.targetNamespace == string.Empty)   //clause 6 - o1 is negation of absent
                    {
                        nslist = o1.Clone();
                    }
                }
                //if it comes here, its not expressible //clause 5
            }
            return(nslist);
        }