[michaeltiller]

But, of course, what is solvable changes and/or is implementation dependent. Modelica doesn't say much on the topic of impulses. In theory, a vendor could support variable index systems along with the ability to resolve impulses. It is a conscious decision not to codify contemporary constraints on solvers/methods into the language. Of course, Sebastien Furic did quite a bit of work along the lines you are describing but he was unable to persuade the group to accept such constraints.