+ import std.math;
  import std.typecons;
- import std.math;
  /*
  Create a function which returns the largest index of an element which
-     is not greater than or equal to the element immediately preceding it. If
? ----

+ is not greater than or equal to the element immediately preceding it. If
-     no such element exists then return -1. The given array will not contain
? ----

+ no such element exists then return -1. The given array will not contain
-     duplicate values.
? ----

+ duplicate values.
- 
-     Examples:
? ----

+ Examples:
-     >>> can_arrange([1L, 2L, 4L, 3L, 5L])
? ----

+ >>> can_arrange([1L, 2L, 4L, 3L, 5L])
-     3L
+ 3L
-     >>> can_arrange([1L, 2L, 3L])
? ----

+ >>> can_arrange([1L, 2L, 3L])
+ -1L
-     -1L
-     
  */
  long can_arrange(long[] arr)