f[n]⁡(z)=𝒟qn⁡f⁡(z)={z-n⁢(1-q)-n⁢∑j=0nq-n⁢j+(j+12)⁢(-1)j⁢[nj]q⁢f⁡(z⁢qj),z≠0,f(n)⁡(0)⁢(q;q)nn!⁢(1-q)n,z=0.