ROOTS

removed unused/obsolete material: some of it was motivated by Isabelle/MMT (e.g. f150253cb201), but is superseded by AFP metadata (TOML);

src/Pure
src/FOL
src/HOL
src/ZF
src/CCL
src/CTT
src/Cube
src/FOLP
src/LCF
src/Sequents
src/Doc
src/Tools