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Multi-target is required for ocamlyacc but is counterproductive for ocamlc.
This is due to ocamldep which declare .cmi as dependencies only when
a .mli file exists.

That work one day because %.cmi was wrongly spelled %cmi, after the
spelling correction that doesn't work anymore. Until now :)

The last commit is also an improvement for -j

en utilisant parser.pre.mly (le seul fichier à modifier)

the verification algorithm must always terminate and be reasonably
performant in practice, but its worst-case complexity is unknown
and probably exponential. What is quite easy when there is only
one recursive definition, becomes difficult when there is a group
of mutually recursive definitions. An educated discussion would
be highly appreciated.

BTW, I had to convert a couple of recursive "logic"s on integers
into an abstract "logic" + axiom. Pretty much all of them supposed
that the argument was non-negative, and thus were non-terminating!