Yes, I see what you mean. In practice, I have only used this trick for "clean and build" rules, which mean that d will never depend on the dependencies of a, b,

Yes, I see what you mean. In practice, I have only used this trick for "clean and build" rules, which mean that d will never depend on the dependencies of a, b, and c, and I take care not to invoke several conflicting rules as the same time on the command line. Maybe make is able to do some magic to avoid this problem since it has some some kind of process management, at least for dealing with "-j" properly in recursive Makefiles. I doubt it though.