"But there was as, you know, from the beginning I was interested also in the aspect of interaction with the environment through understanding of obstacles and the need to avoid collision and the need to create motions around those obstacles. So having resolved the problem in term of reactivity doesn’t mean that we resolved the global problem. Because motion planning requires us to think about a global path. Now, if we think about the computational complexity of this, we realize that this is exponential in the number of degrees of freedom and it is costly to find a path, to plan a path, especially for a robot with many degrees of freedom. I was always interested in finding a way to connect those planning levels, that is the level where we are planning the motion with the levels of execution where those levels are running at very high frequencies. If we think about the control, we need to have a millisecond of control , whereas if we think about a motion planner, well, between the time we find the obstacles and perceive the environment to the time we come up with the new plan, it’s going to take long time. Especially in the ‘80s. What we really tried to do was to create an intermediate level that would allow us to think about this connection between motion planning and control in a way again similar to that of human. The idea that became known as elastic planning is to start with a plan and continuously adjust this plan reactively. Locally by mechanisms really simple as repulsive potential forces, but the trajectory itself is treated as a physical entity with property of elasticity that will make it shorten and adjust to the environment and the changes in the environment. That became a very, very interesting technique that also is being pursued by a number of my current student and previous students like Oliver Brock, who worked on this. Sean Quinlan developed the early version of it, and now a number of new students are working on taking this further, not only to move in the free space, but also to think about the contact space."