1. Let $a\in \mathbb{D}$ and $r\in(0,1)$. Then $\Delta_{ph}(a,r)$ is the Euclidean disc $D(C,R)$, where
    $
    C=\frac{1-r^2}{1-r^2|a|^2}\,a\quad \textrm{and}\quad R=\frac{1-|a|^2}{1-r^2|a|^2}\,r.
    $

2. Let $C\in\mathbb{D}\setminus\{0\}$ and $R\in(0,1-|C|)$. Then the Euclidean disc $D(C,R)$ is the pseudohyperbolic disc $\Delta_{ph}(a,r)$, where
    $
    a=\frac{(1+R^2-|C|^2)-\sqrt{(1+R^2-|C|^2)^2-4|C|^2}}{2|C|^2}C
    $
and
	$
    r=\frac{(1+R^2-|C|^2)-\sqrt{(1+R^2-|C|^2)^2-4R^2}}{2R}.
	$

alkukuvakiekko

A = Intersect(xAxis, yAxis)
B = Point(xAxis)
c = Circle(A, B)
r = 0.63 (slider from 0 to 1, step 0.01)
a = (0.4944503666839651, 0.3466379695133965)
C: ((1 - r^(2)) / (1 - (r^(2) * abs(a)^(2))) * a)
R: ((1 - abs(a)^(2)) / (1 - (r^(2) * abs(a)^(2))) * r)
d = Circle(C, R)
e = Circle(A, r)
b = false