Graphically, mathematical lattices can be depicted as line diagrams that represent a formal concept by a small circle. [See p 181 of the link for a picture.] For each formal g,
the smallest formal concept to whose extent g belongs is denoted by γg, ...
Please correct me if I err, but 'to the extent of which' can be called a 'relative phrase', based on p 186, A Student's Introduction to English Grammar (2005), by Huddleston & Pullum.
My tribulations with it inspired me to Google examples 'to whose extent' for practice.
I know that as a relative determiner, whose = of whom or [of] which.
The quote concerns only objects (and not persons); so whose =
of which. Then:
whose extent = to
Then how do you dissect and parse this relative phrase?