go back to the complicated code equation registration (because of type classes) that was lost in 922586b1bc87; make it even more hackish to get which code equation was used
src/Pure
src/FOL
src/HOL
src/ZF
src/CCL
src/CTT
src/Cube
src/FOLP
src/LCF
src/Sequents
src/Doc
src/Tools