Check if the interpolation lemma is still true given the new semantics

[franconi]

Check if the interpolation lemma is still true given the new semantics: we believe it is true, but it is better to double check.

[franconi]

We can adapt the detailed proof of the interpolation lemma as found in:
Jean-François Baget. RDF Entailment as a Graph Homomorphism. Proc. 4th international semantic
web conference (ISWC), Nov 2005, Galway, Ireland. pp.82-96
https://inria.hal.science/hal-00922476/document