"How to obtain the following using above definitions?"

Referring to https://arxiv.org/pdf/1302.0547.pdf

#1. Get |p| from the first of Eq.(15);

#2. Substitute this |p| into Eq.(4) at V(q)=0 in H(p,q) defined by Eq.(2);

#3. After trivial algebra we obtain Eq.(7), which is the equation in question.

How to obtain the following using above definitions?

Referring to this note by Nick Laskin:

1. Get $|p|$ from the first of Eqations (15);

2. Substitute this $|p|$ into Eq. (4) assuming $V(q)=0$ in the definition of $H(p,q)$ given by Eq.(2);

3. After trivial algebra we obtain Eq. (7), which is the equation in question.