From Eqn. (19.1), we can write

or

(20.1)

This corresponds to a stream function

(20.2)

The expression for yields

	(20.3)
	(20.4)

Here the prime (´) denotes derivative with respect to the independent variables, the quantity can be evaluated in the following way.

	(20.5)

We can choose y =0 line as a streamline and then we can write ψ(x ,0)=0. This entails F (0)=0.