Title: Select the generator part of a list comprehension
Goal: Generalize the function `f/1' by selecting the expression `X <- List', the a new parameter is `K'.
Parameters: [{file,"gen15.erl"},{posrange,{57,65}},{varname,"K"}].
Documentation: The selected expression contains list generators, the result of the transformation would be a syntactically incorrect list comprehension `[2*X || K(List), X>0]', so the refactoring denied the transformation.
