# voltage Gain in BJT

I am reading the book: Problems & Solution of Electronic Devices & Circuits, and on page 119 I got stumped.

They write that :

$$A_V = A_I \cdot \frac{Z_L}{Z_i}= \cdots = \frac{-h_f}{h_i(Y_L+h_o)-h_r h_f}$$

And then they write that for $Y_L =\infty$ $A_V = \frac{-h_f}{h_i h_o -h_r h_f}$

Where $A_V$ is voltage gain, $Y_L$ is the load admittance, and the $h$'s are the $h$ parameters.

What I don't understand is why we get the last relation when $Y_L = \infty$, shouldn't we get $A_V =0 \ for \ Y_L = \infty$.

Perhaps they meant for $Z_L =1/Y_L$, $Z_L = \infty$, but that's not how it's written in the book.

Can someone explain?