haven't thought about it this way before: a factorial of n is the number of distinct lossless functions between two n-sized sets
https://morel.us-east.host.bsky.network/xrpc/com.atproto.sync.getBlob?did=did:plc:fpruhuo22xkm5o7ttr2ktxdo&cid=bafkreidplpl4oypmfpk76n76xlks3k2cdr5lxwodaqu422thxg7ucenyya
