Quickstart guide:
First install Yosys, SymbiYosys, and the solvers. See here for instructions. Then download the core, generate the formal checks and run them:
wget -O picorv32.v https://raw.githubusercontent.com/cliffordwolf/picorv32/master/picorv32.v
python3 ../../checks/genchecks.py
make -C checks -j$(nproc)