2 + 2 = 5 commutative unital semirings

So this is interesting and a bit out of my math ability league. This professor claims, I guess, that 2+2=5. What do the math heads around here think?

Link: https://twitter.com/andrejbauer/stat...184837122?s=21

via International Skeptics Forum https://ift.tt/2CU8x5a