Well the files have not been installed to / but to
/Volumes/localvolume because I have specified to do so...
So it was a mixture of my fault (not looking where I did install it
to) and the installer itself because it allowed me to select another
volume than ROOT. SWI prolog is missing some dylibs when I tried to
launch it from the false location. So it works on a ROOT volume only.
Hope this helps somebody to avoid the same mistake.
By the way it works very well (my last contact with Prolog dates back
Many thanks for all the hints I received,