Modelexpand is not always unique on output vocabularium

[Ingmar Dasseville]

Counterexample:

vocabulary V{
a
b

}

theory T : V {
    a | b.
}

structure S : V {

}

vocabulary VV {

}

include<mx>
procedure main(){
    stdoptions.nbmodels = 0
    printmodels(modelexpand(T,S,VV))
}

[Broes De Cat]

Duplicate of #727.