If we strip whitespaces in the merge sort version you provided and apply same formatting it becomes a 30-liner https://pastebin.com/KmWBMC0M https://pastebin.co

If we strip whitespaces in the merge sort version you provided and apply same formatting it becomes a 30-liner https://pastebin.com/KmWBMC0M https://pastebin.com/KmWBMC0M vs 31 lines of PHP.