!

The ! symbol is used to represent the factorial operation.

When a factorial appears inside a sentence, it's possible to misinterpret the ! as an exclamation mark:

"How many ways of ordering six objects are there?"

"There are 6!"

Two ! symbols together represent the double factorial, multiplying just the odd or even numbers. So juxtaposition doesn't represent composition here: \(x!! \neq (x!)!\)