Using X_Y-pic for arrows:

If the option |[xy]| is used in the | command, or if X_Y-pic [2]³ is already loaded, then the X_Y-pic arrow feature (with the `cmtip' extension) is used to allow a much more general class of arrows, constructed according to the following rules (with examples where they extend the notation used for the standard):

• Basic arrows are composed by combining the variants |23^_|, the tips |<>|||xo`'|, and the connectors |-=.: |.

• The character |/| `negates' the arrow (once or twice) similar to the way || does for relations, and the characters |?+*| are used to mark the arrow with a symbol corresponding to the reflexive, transitive, and reflexive transitive, closures:

  x	|` - / > |
  "x"	"` - / > "

• Each |!| character makes the arrow a bit longer.

  x	| - > |
  "x"	" - > "

  Note: Some arrows are automatically made a bit longer, e.g., the |< >| arrow shown above.

• The form |||| adds the material to the end of the X_Y-pic arrow. All X_Y-pic 〈labels〉 can be used as described in [2, §16], for example,

  x	| - 1 > |
  |"| x|"|	" - 1 > "

  Use this with care!

• The forms |(|x|)| and |[|x|]| insert a break with x in a circle/box, respectively:

  x	|(1) > |
  |"| x|"|	"(1) > "