Very degenerate polynomial submersions and counterexamples to the real Jacobian conjecture

Until recently, the only known examples of non-injective polynomial local diffeomorphisms of the plane were the Pinchuk maps discovered in 1994. These maps have the form $(p,q)$, where p is a fixed polynomial of degree 10, and q satisfies certain relation. The lowest possible degree of q in a Pinchuk map is 25. In 2021, with the same p of a Pinchuk map, another example was given with q of degree 15. Aiming to find different examples, with the first components having lower degrees, we look for polynomials of degree less than or equal to 9 sharing some properties with the polynomial p of a Pinchuk map. We find precisely one polynomial of degree 7 and some ones of degree 9. By using one of the polynomials of degree 9 in the first component we construct a non-injective polynomial local diffeomorphism of the plane, with degree 15.