title: Is a tree with all black nodes a red black tree?
body: <p>It seems the definition on wiki is not precise:</p>
  
  <p><a href="http://en.wikipedia.org/wiki/Red-black_tree#Properties" rel="noreferrer">http://en.wikipedia.org/wiki/Red-black_tree#Properties</a></p>
  
  <p>Is a tree with all black nodes a red black tree?</p>
  
  <p><strong>UPDATE</strong></p>
  
  <p>With the definition of rbtree not so strict,how do we decide whether to print the children of a black node as red or black?</p>