This LaTeX package provides macros to typeset bra-ket notation, as
well as set specifiers, with a single ("|") or a double ("||" or
("\|") vertical bar specifier in between two bracketed parts.  Each
macro comes in a fixed-size version and an expanding version.  If the
package finds itself operating under e-tex, it uses the extended
primitive \middle for more reliable results.

Homepage:
https://www.tug.org/texlive/
