+=============================================+
|/                                           \|
||  Ejecución paso a paso de la calculadora  ||
|\                                           /|
+=============================================+

=======================================================
=======================================================

Ejecución de la calculadora en "5":


+---------------------------------------------------+
| expr ==> term r1                                  |
|         +---------------------------------------+ |
|         | term ==> factor r2                    | |
|         |         +---------------------------+ | |
|         |         | factor ==> num            | | |
|         |         |           +-------------+ | | |
|         |         |           | num ==> '5' | | | |
|         |         |           +-------------+ | | |
|         |         | r2     ==> £              | | |
|         |         +---------------------------+ | |
|         | r1   ==> £                            | |
|         +---------------------------------------+ |
+---------------------------------------------------+
 

En Arbolito:

      expr
       / \
    term  r1
    / \    \
factor r2   £
  |     |
 num    £
  |
 '5'


=======================================================
=======================================================

Ejecución de la calculadora en "5 + 3":


+---------------------------------------------------------------+
| expr ==> term r1                                              |
|         +---------------------------------------------------+ |
|         | term ==> factor r2                                | |
|         |         +---------------------------+             | |
|         |         | factor ==> num            |             | |
|         |         |           +-------------+ |             | |
|         |         |           | num ==> '5' | |             | |
|         |         |           +-------------+ |             | |
|         |         | r2     ==> £              |             | |
|         |         +---------------------------+             | |
|         | r1   ==> '+' term r1                              | |
|         |         +---------------------------------------+ | |
|         |         | '+'                                   | | |
|         |         | term ==> factor r2                    | | |
|         |         |         +---------------------------+ | | |
|         |         |         | factor ==> num            | | | |
|         |         |         |           +-------------+ | | | |
|         |         |         |           | num ==> '3' | | | | |
|         |         |         |           +-------------+ | | | |
|         |         |         | r2     ==> £              | | | |
|         |         |         +---------------------------+ | | |
|         |         | r1   ==> £                            | | |
|         |         +---------------------------------------+ | |
|         +---------------------------------------------------+ |
+---------------------------------------------------------------+

En Arbolito:

         expr
        /    \
       /      \
   term        r1
    / \       / | \
   /   \     /  |  \
factor r2 '+' term r1
   |   |       / \   \
  num  £   factor r2  £
   |         |    |
  '5'       num   £
             |
            '3'

=======================================================
=======================================================

Ejecución de la calculadora en "5 * 3":

+-----------------------------------------------------------------+
| expr ==> term r1                                                |
|         +-----------------------------------------------------+ |
|         | term ==> factor r2                                  | |
|         |         +-----------------------------------------+ | |
|         |         | factor ==> num                          | | |
|         |         |           +-------------+               | | |
|         |         |           | num ==> '5' |               | | |
|         |         |           +-------------+               | | |
|         |         | r2     ==> '*' factor r2                | | |
|         |         |           +---------------------------+ | | |
|         |         |           | '*'                       | | | |
|         |         |           | factor ==> num            | | | |
|         |         |           |           +-------------+ | | | |
|         |         |           |           | num ==> '3' | | | | |
|         |         |           |           +-------------+ | | | |
|         |         |           | r2     ==> £              | | | |
|         |         |           +---------------------------+ | | |
|         |         +-----------------------------------------+ | |
|         | r1   ==> £                                          | |
|         +-----------------------------------------------------+ |
+-----------------------------------------------------------------+
 

En Arbolito:

         expr
        /    \
     term     r1
    /    \      \
factor    r2     £
  |      / | \
  |     /  |  \
 num '*' factor r2
  |        |    |
 '5'      num   £
           |
          '3'