x > 0, x >0, x > = 0, x >= 0, x < 0, x : 0, X : 0, x=0, x ≥ 0, x = 0, ∀x ∈ (0, |x| = 0, (x - 0, x ∈ (0; π), x # 0 ), X:0, X: 0, φ= x=0, X–(0, x≠0, X = {0};, x = 0 …