All arithmetic expressions can be written using any of these representations.
However, postfix representation combined with a stack of registers is the most
efficient means to evaluate arithmetic expressions. In fact, some electronic calculators
(such as Hewlett-Packard) require the user to enter expressions in postfix
notation. With a little practice on these calculators, it is possible to rapidly evaluate
long expressions containing many nested parentheses without ever stopping to
think about how terms are grouped.
Consider the following expression: