1. in is supposed to be O(lg(n)) or better. Generic code may depend on this property. Searching an array is O(n).
Probably it should work if we're using a "SortedRange".
int[] a = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]; auto p = assumeSorted(a); assert(3 in p);