Given the set A = {(x, y) ∈ R2 | x2 +
y2 < 1 and y ≥ 0}. Draw sketches of cl A, int A, ∂A,
(cl(Ac))c, the limit points of A, and the
isolated points of A. Try to be clear about what the sketch is
describing. (The answer does not depend on whether one uses the
Euclidean distance or the taxi distance on R2.)