I have looked into the Isabelle tutorial which presents an example of it's use in verifying security protocol. However, it is a bit out of my understanding as I only know the basics. I'm looking for some examples which are not just simple theorems but practical applications using Isabelle/HOL. For example proving some algorithms or may be verifying properties system or some non-trivial mathematical theorem. Are such examples available anywhere ?
I have looked into the list of all applications provided in the isabelle official page but most of them are proofs of theorems.
I am also looking at an example of a file system verification using Alloy. It provides a proof where the properties of file/directories can be verified. I'm looking for something similar to it.