Linear logic uses an unusual symbol, an ampersand rotated 180 degrees, for multiplicative disjunction.
The symbol is U+214B in Unicode.
I was looking into how to produce this character in LaTeX when I found that the package
cmll has two commands that produce this character, one semantic and one descriptive:
This got me to wondering how you might create a symbol like the one above if there wasn’t one built into a package. You can do that by using the
graphicx package and the
\rotatebox command. Here’s how you could roll your own par operator:
There’s a backslash in front of the & because it’s a special character in LaTeX. If you wanted to rotate a K, for example, there would be no need for a backslash.
\rotatebox command can rotate any number of degrees, and so you could rotate an ampersand 30° with
to produce a tilted ampersand.
 The name
\parr comes from the fact that the operator is sometimes pronounced “par” in linear logic. (It’s not simply
\par because LaTeX already has a command
\par for inserting a paragraph break.)
\invamp is short for “inverse ampersand.” Note however that the symbol is not an inverted ampersand in the sense of being a reflection; it is an ampersand rotated 180°.