ASCIIfying the formatting is not idempontent

[lukacslacko]

ASCIIfying then formatting results in this diff:

-    (¬y = x + Z; Z).↺ | deduce
+    (¬y = x + Z; Z)↙induction> | deduce

I think it's as simple as moving ".<" below the "<...>" entries in PREFIXES in lexer.rs.

[lukacslacko]

It's more complicated :) The ordering of ., .< and <induction> always seem to either cause .< not be interpreted as ↙ or .<induction> interpreted as ↙induction>. I guess some lookahead would be needed in the lexer.rs? I'm not sure.