The Task
Leading on from the first challenge.
Write some code to output all letters of the alphabet from a-z and back down to a in lowercase. Then b-z in uppercase back to a in uppercase too. The output should be:
If you want your solution benchmarked against others, please provide it in PHP (benchmarking PHP vs JS is too much hassle!)
abcdefghijklmnopqrstuvwxyzyxwvutsrqponmlkjihgfedcbaBCDEFGHIJKLMNOPQRSTUVWXYZYXWVUTSRQPONMLKJIHGFEDCBA
Post all solutions below, fastest and shortest solution wins.