GUILE, GNU's Ubiquitous Intelligent Language for Extension, is a library that implements the Scheme language plus various convenient facilities. It's designed so that you can link it into an application or utility to make it extensible. Our plan is to link this library into all GNU programs that call for extensibility. This is guile 2.0, which became old in 2017. It is installed in a guile/20 sub-prefix.