I have a List with Integers and anonymous variables and I try to find the index of a special values. Problem is as soon I'm using `nth1/3` to find the indices Prolog assigns values to the anonymous variables and therefore I find way too indices. 

Example:
`List = [1,\_,1]`, where I want as result `X = 1, X = 3` from `nth1(X,List,1)`, but as stated before I get `X = 1, X = 2, X = 3`.