If.txt

          +~~~~~~~~~~~~~~~~~+
          :                 :
          :   $1 = eval c   :
          :                 :
          +~~~~~+~~~~~+~~~~~+
                |     |
         +------+     +-------+
         v                    v
 +-------+-------+    +-------+--------+
 |               |    |                |
 |   assume $1   |    |   assume !$1   |
 |               |    |                |
 +-------+-------+    +-------+--------+
         |                    |
         v                    v
+~~~~~~~~+~~~~~~~~+  +~~~~~~~~+~~~~~~~~+
:                 :  :                 :
:   $2 = eval t   :  :   $2 = eval f   :
:                 :  :                 :
+~~~~~~~~+~~~~~~~~+  +~~~~~~~~+~~~~~~~~+
         |                    |
         +-------+    +-------+
                 v    v
          +------+----+------+
          |                  |
          |   $result = $2   |
          |                  |
          +------------------+