There is a non-constant continuous function from the open unit disc $$D = \{ z \in \mathbb{C} \mid |z| < 1 \}$$ to $\mathbb{R}$ which takes only irrational values.
There is a non-constant continuous function from the open unit disc
$$D = \{ z \in \mathbb{C} \mid |z| < 1 \}$$
to $\mathbb{R}$ which takes only irrational values.