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(*         Gardens Point Modula-2 Library Definition            *)
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(*     (c) Copyright 1992 Faculty of Information Technology     *)
(*              Queensland University of Technology             *)
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(*     Permission is granted to use, copy and change this       *)
(*     program as long as the copyright message is left intact  *)
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DEFINITION MODULE CardTrees;
  FROM CardSequences IMPORT Sequence;

  TYPE Tree; (* pointer to root, or NIL for empty tree *)

  PROCEDURE InitTree(VAR tre : Tree);
  (* postcondition : tre is an empty tree *)

  PROCEDURE IsEmpty(tre : Tree) : BOOLEAN;
  (* postcondition : returns "tre is the empty Tree" *)

  PROCEDURE Insert(VAR tre : Tree; element : CARDINAL);
  (* precondition : tre is a valid tree, possibly empty   *)
  (* postcondition: element is in tree & tree is ordered  *)

  PROCEDURE Delete(VAR tre : Tree; element : CARDINAL);
  (* precondition : tre is a valid ordered tree, or empty *)
  (* postcondition: element not in tree, tree still valid *)

  PROCEDURE Lookup(tre : Tree; element : CARDINAL) : BOOLEAN;
  (* precondition : tre is a valid ordered tree, or empty *)

  PROCEDURE MakeSequence(tre : Tree; VAR seq : Sequence);
  (* postcondition : seq has preorder contents of tre *)

END CardTrees.
