// C#

  System.Collections.Hashtable ht
    = new System.Collections.Hashtable (100);
  ...
  if (ht.ContainsKey (key)) {
    ...
  }
  ...

;;; Scheme

  (let ((ht (System.Collections.Hashtable. 100)))
    ...
    (if (.ContainsKey ht key)
        ...)
    ...)