Consider the claim:

Solving the general constraint problem in an isochronal WR solver is in the category of hard problems. Before the problem was solved by LuckGrib, it may have been in the category of what many considered to be an impossible problem. It is certainly difficult.

There are a couple of WR systems available which provide the ability for their WR solvers to navigate to a series of points, point A to point B, point B to point C, and so on. This is only useful when you are required to pass through or close by each of those points.

Consider this image, where two constraint points are specified:

Many of the routes, including the highlit one, are finding optimum solutions that do not pass close by the constraint points. In a system that routes from point A to point B to point C, these solutions would not be found.

Generalized constraints, which can be left to port or left to starboard are superior to these other simple systems.

A well known product called Expedition can solve these problems, but only when using its grid solver.

From the Expedition manual, March/2021.

If anybody knows of another system which can solve these problems, please let me know.

First, maybe not last?

Its often interesting to watch a group of software developers make progress. If the group considers a problem as not being possible, then nobody will spend any time on it. Once a problem has been solved, as LuckGrib has now done with its generalized point constraint isochrone solver, then all other developers now see that this problem is solvable. LuckGrib has provided an existence proof that isochrone solvers can be used in these situations.

LuckGrib was first. It will be interesting to see who comes along next.

One, Two, Three - Go!