title: deletion on B+ tree
body: <p>As a student, I've been trying to implement B+ tree in C myself. The insert is ok but the deletion holds me off. One of my questions is this:
  Is it ok to remain a key in the internal node while its key in the leaf node has been deleted?
  This may happen when the internal node is not the leaf's parent.
  Is my description clear enough? Does any one have similar experiences?</p>