Add mapsfrom and mapsfrom.long

[fee1-dead]

Refs: mapsfrom mapsfrom.long

Since this was easy enough I thought I'd just open a PR. Will discuss on Discord as well!

[Enivex]

I would prefer mapsfrom and mapsfrom.long for semantic reasons.

[fee1-dead]

Ah, it also matches stmaryrd's LaTeX command. Would there be any value in keeping mapsto.rev as an alias though? Since mapsto is much more wellknown and my first instinct is to type mapsto.rev.

[Enivex]

I don't think an alias pulls its own weight, especially because it's already an alias for arrow.l.bar. That's three names for the same symbol.

As an alternative, how about

maps
  .to ↦
  .to.long ⟼
  .from ↤
  .from.long ⟻

(There are bunch more arrows too)

Now you get discoverability, and less duplication. The cost being a period for the full name, but you would in fact be able to use the shorter maps and maps.long for the most common use case (or the shorthand).

[MDLC01]

My main concern with this is that mapsto was added as an alias because it is a very common symbol. But in my experience, I don't think I've ever seen ↤ in the wild. For this reason, I think keeping it as arrow.l.bar is okay.

Regarding @Enivex's proposal, "maps.to" is more annoying to write than "mapsto" (on my AZERTY keyboard, that's two additional key presses) and "maps" alone feels less readable. But if we decide to add a special name for ↤, I don't have a strong opinion on any on the options that were mentioned in this thread.

[knuesel]

I also don't have a strong opinion but one downside of x maps y is that it looks semantically incorrect: it reads as if x is mapping y while it's being mapped to y.

[fee1-dead]

I think after considering the comments above, the consensus roughly lies on mapsfrom since the downside of maps/maps.to have been given. So I have tentatively changed this to add mapsfrom.