SHOW: Show the contents of string variables including any variables
nested within them
syntax: SHOW(x)
Where x can be any valid math expression or any combination of string variables
For example: the variable $A can contain the string "deriv($B, x, -3)" and
the command SHOW($A) would show the contents of the variable $B within the
expression. For example if $B currently contains "-x^2 + 10" then SHOW($A)
would display "deriv(-x^2 + 10, x, -3)".