public struct KeyValuePair[X,Y]
{
  public this (_x : X, _y :  Y)
  { }
}

public interface IComparer[T]
{
   Compare (mutable  x : T) : int;
}

public class KeyValuePairComparer[K,V] : IComparer[KeyValuePair[K,V]]
{
  public Compare (_a : KeyValuePair[K,V]) :  int
  {
     0;
  }
}

public class TreeBag[T]
{
   mutable  comparer : IComparer[T];
   mutable  item : T;

  public this (mutable  comparer : IComparer[T],mutable  item :  T)
  {
    this.comparer = comparer;
    this.item = item;
  }

  public Find () :  int
  {
     comparer.Compare (item);
  }
}

public class X
{
  public static Main () :  void
  {
    mutable  pair =  KeyValuePair (3, 89);
    mutable  comparer =  KeyValuePairComparer ();
    mutable  bag =  TreeBag (comparer, pair);
    _ = bag.Find ();
  }
}
/*
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*/