User blog comment:MilkyWay90/Finishing my very first notation - The Generalized Factorial/@comment-35470197-20190710234255/@comment-35470197-20190713062826

> How exactly?

The rule applicable to expressions including two exclamation marks is the rule for \(F_!(!,l,!)\). Namely, you can apply it only to \((!,1,\ldots,1,!)\), but not to \((3,!,3,3,!)\).