One solution could be adding a `sort` argument (which takes a function that compares two `<T>` items and returns `true` or `false` depending on their order) to

One solution could be adding a `sort` argument (which takes a function that compares two `<T>` items and returns `true` or `false` depending on their order) to all functions on unordered collections of `<T>` items in which an order must be chosen, or requiring that the items in such collections implement a `TotalOrder` interface or something similar. This isn't very ergonomic in languages that don't have an equivalent of Traits or typeclasses though. In languages which permit side effects, this would include any functions that iterate over the items in an unordered collection.