instead of constructing a list of LTSs,we just collect the information, and construct LTS on demand
TODO probably we can slightly change the interface to constrcutLTS
and pass it an index, and let it lookup the right trace and diff
from the corresponding lists.
TODO fix the combinedLTS
(should we just create it right away?
on the fly as we also create the string-result, and
the trace+diff for the test-purposes?
or is creating it too expensive?)