tan(x) >= -1
pi 3*pi [0, --) U [----, pi] 2 4
x in Union(Interval.Ropen(0, pi/2), Interval(3*pi/4, pi))
/ / pi\ /3*pi \\ Or|And|0 <= x, x < --|, And|---- <= x, x <= pi|| \ \ 2 / \ 4 //
((0 <= x)∧(x < pi/2))∨((x <= pi)∧(3*pi/4 <= x))