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#### 3.7.3 RPN Tutorial Exercise 3

The <TAB> key provides a way to operate on the number in level 2.

         3:  10         3:  10         4:  10         3:  10         3:  10
         2:  20         2:  30         3:  30         2:  30         2:  21
         1:  30         1:  20         2:  20         1:  21         1:  30
             .              .          1:  1              .              .
                                           .

                           <TAB>             1              +             <TAB>

Similarly, `M-<TAB>` gives you access to the number in level 3.

         3:  10         3:  21         3:  21         3:  30         3:  11
         2:  21         2:  30         2:  30         2:  11         2:  21
         1:  30         1:  10         1:  11         1:  21         1:  30
             .              .              .              .              .

                           M-<TAB>           1 +           M-<TAB>          M-<TAB>