evade a potential conflict of /bin/bash versus /bin/sh -> dash (notably on Ubuntu and Debian) -- note that execvpe does not exist on old glibc on Ubuntu 10.04 LTS, but the environ should be unchanged;
src/Pure
src/FOL
src/HOL
src/ZF
src/CCL
src/CTT
src/Cube
src/FOLP
src/LCF
src/Sequents
src/Doc
src/Tools