According to the author, x=ln(y) should go through y=1, not x=1, making the plot look similar to a half U on the positive side of the x-axis, instead of a half C, on the the positive side of the y-axis.
var('y')
f=ln(y)
plot(f, (x,-5,5), ymin=-5, ymax= 5, aspect_ratio=1)
