Title: Select a simple subexpression
Goal: Generalize function `double/1' by selecting the subexpression `2' and the name of the new argument is `N'.
Parameters: [{file,"gen1.erl"},{posrange,{60,60}},{varname,"N"}].
Documentation: There is not any variable with the name `N' in the body of `double/1', so it is possible to introduce a new variable and replace the subexpression `2' with that variable. `double/1' is exported from the module, so a new function (`double/1') is created to preserve the original interface of the module.
