Others have already discussed the logic for the input values you present at the beginning. I'm more concerned about the general functionality of your code. To be specific, did you really mean to exclude the case where the difference values are equal to 1 from your logic? For those boundary conditions, all of the expressions will fail, because 1 is neither less than nor greater than 1.
If your /[abc]to[abc]/ vars are intended to describe absolute distances, I would recommend going with the abs() value as previously recommended, then using >=1 or <=1 for one of the two cases. You probably haven't seen it yet if your data is really real, but it could burn you in the future.