À­¸ñÀÊÈÕ·´Ñݹ«Ê½(lagrange inversion)×éºÏÖ¤Ã÷

There is a simple combinatorial proof. The original form is $$ [t^n]w^k=\frac{k}{n}[t^{n-k}]\phi^n $$ where $w=t\phi(w)$ consider $w$ as egf. of the w