This package defines the command \perfectcut#1#2 which displays a bracket <#1||#2>. Various delimiters are similarly defined. The effect of these commands is to let the delimiters grow according to the number of nested \perfectcommands (regardless of the size of the contents). The package is originally intended for solving a notational issue regarding the representation of abstract-machine-like calculi in proof theory and computer science. For general use, the package also defines commands for defining custom delimiters that behave in the same way. This package also offers a sound reimplementation of \big, \bigg, etc.