In the derivation of u at the beginning of Unit 4.1 the matrix shown is missing a minus sign in the fourth row first column it shows l-w when it should be -l-w. This is small enough that it doesn’t show up in exercise 4.2 there is no noticeable difference between the animated gif and the robots movement that I overlooked it. It wasn’t until exercise 4.3 that I noticed something was not quite right and spent hours working on my code. Finally gave up and looked at the solution it still took me awhile to find. This was only the second time I have looked at a solution before getting it right on my own.