I am reading Topics on Superfulidity of Walter Greiner Book Titled "Quantum:Mechanics Special Chapters" In Exercise page no 200, Hamiltonian has been discussed and derived throughly using commutation relation . I understood very nicely but equation 4 and 5 is where I am stucked on extra v[squared] Term. Here is the equation
and Using the relation
Equation 5 is derived from above equation as below
term appeared in 2nd term of equaiton 5.
Thanks in advance.