Union between two lists doesn't work

Union and Intersect doesnt work accomplished using for loop

@page "/SetTheory"
 
@using System.ComponentModel.DataAnnotations;  
 
  
<PageTitle>Set Theory</PageTitle>
 <div>
           SET A
  </div>
<ul>
    @foreach (var todo in todos)
    {
        <li>
            <input type="checkbox"  @bind="todo.IsDone" />
            <input  readonly @bind="todo.Title"  />
        </li>
    }
</ul
<input placeholder="Add a Number" @bind="newTodo" />
<button @onclick="AddTodo">Add Set A</button> <br>
<button @onclick="DeleteAll">Clear All Set A</button> <br>
<button @onclick="DeleteTodo">Delete Set A  </button>
<div>
           Ascending Order  
  </div>
 <ol>
    @foreach (var todo in  listsort)
    {
         <li style="display:inline"> 
            
            <input readonly @bind="todo.Title" />
           
        </li>
    }
</ol>
         <br />
         <ul>
    @foreach (var todob in todosb)
    {
        <li >
            <input type="checkbox"  @bind="todob.IsDone" />
            <input  readonly @bind="todob.Title"  />
        </li>
    }
</ul>
 
<div>
           SET B
  </div>
<input placeholder="Add a Number Set B" @bind="newTodob" />
<button @onclick="AddTodoB">Add Set B</button> <br>
<button @onclick="DeleteAllB">Clear All Set B</button> <br>
<button @onclick="DeleteTodoB">Delete Set B  </button>
 
 <ol>
    @foreach (var todob in  listsortb)
    {
        <li style="display:inline">
            
            <input readonly @bind="todob.Title" />
           
        </li>
    }
</ol>
          <br />
 <button @onclick="Submit">Perform Calculation</button>
 
         <br />
          <div> A - B </div>
          
  <ul>
     @if(aminusblist.Count()==0)
     {<span>Empty Result</span>}
                   
         @foreach (var aminusb in  aminusblist)
    {
        <li>
            
            @aminusb.Title
           
        </li>
    }
           
 
</ul>
<br/>
 <div> B - A </div>
<br/>
<ul>
         @if(bminusalist.Count()==0)
     {<span>Empty Result</span>}
                   
         @foreach (var bminusa in  bminusalist)
    {
        <li>
            
            @bminusa.Title
           
        </li>
    }
           
 
</ul>
 <br/>
<span> A Union B </span> 
 <br/>
    @if(unionlist.Count()==0)
     {<span>Empty Result</span>}
<ul>
     
                   
         @foreach (var unionlst in   unionlist)
    {
        <li>
            
            @unionlst.Title
           
        </li>
    }
           
 
</ul>
 <br/>
<span> A Intersection B </span> 
 <br/>
    @if(interlist.Count()==0)
     {<span>Empty Result</span>}
<ul>
     
                   
         @foreach (var interlst in   interlist)
    {
        <li>
            
            @interlst.Title
           
        </li>
    }
           
 
</ul>
<div>
  
        @errmsg
    </div>
 
@code {
    public class TodoItem
    {
        public int Title { get; set; }
        public bool IsDone { get; set; }
    }
    public class TodoItemB
    {
        public int Title { get; set; }
        public bool IsDone { get; set; }
    }
    public class  Groups
    {
        public int Title { get; set; }
    }
    public class  GroupsA
    {
        public int Title { get; set; }
    }
    public class  GroupsB
    {
        public int Title { get; set; }
    }
    public class  UnionList
    {
        public int Title { get; set; }
    }
    public class  CommonList
    {
        public int Title { get; set; }
    }
    public class  AminusBList
    {
        public int Title { get; set; }
    }
    public class  Summary
    {
        public int Title { get; set; }
        public int cnts { get; set; }
    }
    private List<TodoItem> todos = new();
    private List<TodoItem> listsort = new();
    private List<TodoItemB> todosb = new();
    private List<TodoItemB> listsortb = new();
    private int newTodo;private int newTodob; int rancnta; int rancntb; int meansum; int maxnum;int minnum; int val1;int val2; int val0;
    private string errmsg;private string skipa;private string skipb; private int max;private int ran; private decimal calcmean; private decimal calcmedian; int median = 0; private int[] myNum = { 0  }   ; 
    private List<Groups> modegroups = new();private List<GroupsA>  groupsa = new();private List<GroupsB>  groupsb = new(); private List<CommonList>  unionlist = new(); private List<CommonList>  aminusblist = new();private List<CommonList>  bminusalist = new();private List<CommonList>  interlist  = new();
    private List<Groups> tempgroups = new(); private string display = "N"; private int[] medarr; private int[] groupaarr; private int[] groupbarr; private int[] commonarr; private int[] aminusb ={ 0  }   ; 
    private List<Summary> sumgroups = new();private string displayaminusb;
    private List<CommonList>  remlist  = new();
    protected override void OnInitialized()
    {
    }
    private void DeleteAll()
    {
        int rem = todos.Count();
        if (rem > 0)
        {
            todos.Clear();
            listsort.Clear();    aminusblist.Clear(); bminusalist.Clear();unionlist.Clear();interlist.Clear();
        }
        else
        { errmsg = "No records to Delete";}
    }
    private void DeleteTodo()
    {
        display = "N";  
        ran = 0;maxnum = 0;minnum= 0;    errmsg = "";
        rancnta = 0; rancntb = 0;meansum = 0; calcmean = 0;calcmedian = 0; val0 =0;val1 = 0;val2 = 0;
        int rem = todos.Count((s => s.IsDone == true));
        if (rem > 0)
        { aminusblist.Clear();bminusalist.Clear();unionlist.Clear();interlist.Clear();
            var toRemove = todos.Where(todos => todos.IsDone == true).ToList();  
            foreach (var s in toRemove)
            {
                todos.Remove(s);
            }
        }
        else
        { errmsg = "Select a number to Delete";}
        listsort = todos.OrderBy(p => p.Title).ToList();
        groupsa =  listsort.Select( g => new GroupsA { Title = g.Title  } ).ToList();
    }
    private void AddTodo()
    {     display = "N";
        myNum[0] = 0;maxnum = 0;minnum= 0;  val0 =0; val1 = 0;val2 = 0;
        aminusblist.Clear();bminusalist.Clear();unionlist.Clear();interlist.Clear();
        ran = 0;
        rancnta = 0; rancntb = 0;meansum = 0;calcmean = 0;calcmedian = 0;
        errmsg = "";
        skipa = "N";
        errmsg = "";
        var resultx = todos.FirstOrDefault(c => c.Title == newTodo);
        if(resultx == null)
        { skipa = "N";}
        else  { skipa = "Y";errmsg = "Cannot Allow duplicates";}
        if( (newTodo <  0) ||   (newTodo > 100)) 
        { skipa = "Y"; 
            errmsg = "Enter number between 0 and 100";}
        int cnt  = todos.Count();
        if (cnt>20)
        {   skipa = "Y"; 
            errmsg = "Cannot enter number more than 20 numbers";}
        if(skipa=="N")
        { 
            todos.Add(new TodoItem { Title = newTodo });
        }
        newTodo = 0;
        listsort = todos.OrderBy(p => p.Title).ToList();
        groupsa =  listsort.Select( g => new GroupsA { Title = g.Title  } ).ToList();
    }
    private void DeleteAllB()
    {
        int rem = todosb.Count();
        errmsg = "";
        if (rem > 0)
        { aminusblist.Clear();bminusalist.Clear();unionlist.Clear();interlist.Clear();
            todosb.Clear();
            listsortb.Clear();
        }
        else
        { errmsg = "No records to Delete";}
    }
    private void DeleteTodoB()
    {
        display = "N";  
        ran = 0; 
        rancnta = 0; rancntb = 0; 
        int rem = todosb.Count((s => s.IsDone == true));
        aminusblist.Clear();bminusalist.Clear();unionlist.Clear();interlist.Clear();
        sumgroups.Clear();
        if (rem > 0)
        {
            var toRemoveb = todosb.Where(todos => todos.IsDone == true).ToList();  
            foreach (var s in toRemoveb)
            {
                todosb.Remove(s);
            }
        }
        else
        { errmsg = "Select a number to Delete";}
        listsortb = todosb.OrderBy(p => p.Title).ToList();
        groupsb =  listsortb.Select( g => new GroupsB { Title = g.Title  } ).ToList();
    }
    private void AddTodoB()
    {     display = "N";
        myNum[0] = 0;maxnum = 0;minnum= 0;  val0 =0; val1 = 0;val2 = 0;
        aminusblist.Clear();bminusalist.Clear();unionlist.Clear();interlist.Clear();
        ran = 0;
        rancnta = 0;rancntb = 0;meansum = 0;calcmean = 0;calcmedian = 0;
        errmsg = "";
        skipb = "N";
        errmsg = "";
        var resultx = todosb.FirstOrDefault(c => c.Title == newTodob);
        if(resultx == null)
        { skipb = "N";}
        else  { skipb = "Y";errmsg = "Cannot Allow duplicates";}
        if( (newTodob <  0) ||   (newTodob > 100)) 
        { skipb= "Y"; 
            errmsg = "Enter number between 0 and 100";}
        int cntb  = todosb.Count();
        if (cntb>20)
        {   skipb = "Y"; 
            errmsg = "Cannot enter number more than 20 numbers";}
        if(skipb=="N")
        { 
            todosb.Add(new TodoItemB { Title = newTodob });
        }
        newTodob = 0;
        listsortb = todosb.OrderBy(p => p.Title).ToList(); 
        groupsb =  listsortb.Select( g => new GroupsB { Title = g.Title  } ).ToList();
    }
    private void Submit()
    { displayaminusb = "N"; aminusblist.Clear();bminusalist.Clear();unionlist.Clear();interlist.Clear();
        errmsg = "";
        rancnta = todos.Count();
        rancntb = todosb.Count();
        var tempgroupsa = groupsa.Select(n => n.Title).ToList();
        groupaarr = tempgroupsa.ToArray();
        var tempgroupsb = groupsb.Select(n => n.Title).ToList();
        groupbarr = tempgroupsb.ToArray();
        var n = groupaarr.Length;
        var m = groupbarr.Length;
        //A-B
        for (int i = 0; i < groupaarr.Length; i++)
        {
            var resulty = groupsb.FirstOrDefault(c => c.Title == groupaarr[i]);
            if (resulty == null)
            { displayaminusb = "Y";
                aminusblist.Add(new CommonList { Title = groupaarr[i] });
            }
        }
        int aminuscount = aminusblist.Count();
        if(aminuscount==0)
        { errmsg = "Empty Result "; }
        if(n==0)
        {errmsg = "Empty Set A ";}
        //B-A
        for (int i = 0; i < groupbarr.Length; i++)
        {
            var resultz = groupsa.FirstOrDefault(c => c.Title == groupbarr[i]);
            if (resultz == null)
            { displayaminusb = "Y";
                bminusalist.Add(new CommonList { Title = groupbarr[i] });
            }
        }
        int bminusacount = bminusalist.Count();
        // A Union B   
        for (int i = 0; i < groupaarr.Length; i++)
        {
            unionlist.Add(new CommonList { Title = groupaarr[i] });
        }
        for (int i = 0; i < groupbarr.Length; i++)
        {
            var resultx = unionlist.FirstOrDefault(c => c.Title == groupbarr[i]);
            if (resultx == null)
            {  
                unionlist.Add(new CommonList { Title = groupbarr[i] });
            }
        }
        unionlist =  unionlist.OrderBy(p => p.Title).ToList(); 
        int unioncount = unionlist.Count();
        // A Intersection B   
        for (int i = 0; i < groupaarr.Length; i++)
        {
            var resultn = groupsb.FirstOrDefault(c => c.Title == groupaarr[i]);
            if (resultn != null)
            {
                interlist.Add(new CommonList { Title = groupaarr[i] });
            }
        }
      
    }
    }