Title: Supporting selection of lhs containing several variables
Goal: Generalize the function `f/1' by selecting the expression `[X, {[Y], Z}]'.
Parameters: [{ask_missing,true},{file,"gen40.erl"},{posrange,{45,57}}]. 
Documentation: Generalize function `f/1' from the left-hand side of expression `[X, {[Y], Z}] = [2, {[3], 4}]'.
