This forced  me to put  everything into contracts,  without expanding
nodes, which required more fixes. Sigh.

(which was actualy already there for the diameter)

nb : it currently fails as the legitimate predicate is wrong.

(not yet finished: the legitimate predicate is not rigth)

the same as the one used in State.to_string (in state.ml)

and so that all daemons have the same interface, which makes
the use of run-kind2.sh easier.

This is necessary  to compute the heigth in a  tree and will probably
be useful for other purposes