PSL for Isabelle2021

This release should be compatible with Isabelle2021.

Note that the directory layout has been changed from Isabelle2020 to Isabelle2021.
Therefore, one needs to use the command similar the following to use PSL and all that.

(path to the Isabelle binary)isabelle jedit -d (path to the directory that contains this README file) -l Smart_Isabelle

Other news:

• SeLFiE and sem_ind have made LiFtEr and smart_induct obsolete.

If you encounter problems, please send a message to the main developer, Yutaka Ng.