Question Number 58965 by arcana last updated on 02/May/19
$$\mathrm{if}\:{a},{b}\:\in\mathbb{C}\:\mid\:\mid{a}\mid<\mathrm{1},\mid{b}\mid<\mathrm{1} \\ $$$$\Rightarrow\mid\frac{{a}−{b}}{\mathrm{1}−\bar {{a}b}}\mid<\overset{} {\mathrm{1}} \\ $$
if-a-b-C-a-lt-1-b-lt-1-a-b-1-a-b-lt-1-