Sample insertion sequence for a smallish AVL tree.  Note that I printed
the left side first; if you rotate your head 90 degrees counter-clockwise
it will have the correct orientation.

insert:10
EQUALHT:10
----------------------------------------
insert:30
   EQUALHT:30
RIGHTHI:10
----------------------------------------
insert:20                                triggers a single rotation to the left
   EQUALHT:30
EQUALHT:20
   EQUALHT:10
----------------------------------------
insert:25
   LEFTHI:30
      EQUALHT:25
RIGHTHI:20
   EQUALHT:10
----------------------------------------
insert:27                                 triggers a left-right double rotation
      EQUALHT:30
   EQUALHT:27
      EQUALHT:25
RIGHTHI:20
   EQUALHT:10
----------------------------------------
insert:15
      EQUALHT:30
   EQUALHT:27
      EQUALHT:25
EQUALHT:20
      EQUALHT:15
   RIGHTHI:10
----------------------------------------
insert:12                                triggers a right-left double rotation
      EQUALHT:30
   EQUALHT:27
      EQUALHT:25
EQUALHT:20
      EQUALHT:15
   EQUALHT:12
      EQUALHT:10
----------------------------------------
insert:21
      EQUALHT:30
   LEFTHI:27
      LEFTHI:25
         EQUALHT:21
RIGHTHI:20
      EQUALHT:15
   EQUALHT:12
      EQUALHT:10
----------------------------------------
insert:23                                 triggers a left-right double rotation
      EQUALHT:30
   LEFTHI:27
         EQUALHT:25
      EQUALHT:23
         EQUALHT:21
RIGHTHI:20
      EQUALHT:15
   EQUALHT:12
      EQUALHT:10
----------------------------------------
insert:26                                 triggers a left-right double rotation
         EQUALHT:30
      EQUALHT:27
         EQUALHT:26
   EQUALHT:25
      LEFTHI:23
         EQUALHT:21
RIGHTHI:20
      EQUALHT:15
   EQUALHT:12
      EQUALHT:10
----------------------------------------
insert:13
         EQUALHT:30
      EQUALHT:27
         EQUALHT:26
   EQUALHT:25
      LEFTHI:23
         EQUALHT:21
EQUALHT:20
      LEFTHI:15
         EQUALHT:13
   RIGHTHI:12
      EQUALHT:10
----------------------------------------
insert:14                                triggers a left-right double-rotation
         EQUALHT:30
      EQUALHT:27
         EQUALHT:26
   EQUALHT:25
      LEFTHI:23
         EQUALHT:21
EQUALHT:20
         EQUALHT:15
      EQUALHT:14
         EQUALHT:13
   RIGHTHI:12
      EQUALHT:10
----------------------------------------
insert:17                                triggers a single rotation to the left
         EQUALHT:30
      EQUALHT:27
         EQUALHT:26
   EQUALHT:25
      LEFTHI:23
         EQUALHT:21
EQUALHT:20
         EQUALHT:17
      RIGHTHI:15
   EQUALHT:14
         EQUALHT:13
      EQUALHT:12
         EQUALHT:10
----------------------------------------