title: How to know if a binary tree is ordered scheme
body: <p>A binary tree is ordered if all its children are under the left branch 
  that the data of the root and branch of the right age and, in turn, binary trees 
  of the left and right branches are also sorted. Write the procedure 
  (ordered-btree? btree) receiving a binary tree as argument and returns 
  True if ordered and false if not.</p>
  
  <p>How can I do this?</p>