Set of functions....
Θ(g(n)) = { f(n) : there exist positive constants c1, c2, and n0 such that
0 ≤ c1g(n) ≤ f(n) ≤ c2g(n)       for all n ≥ n0 }
Ω - remove c2g(n) term from consideration in inequality above; remaining c1 just referred to as c in defn

O - remove c1g(n) term from consideration in inequality above; remaining c2 just referred to as c in defn