I am trying to teach myself asymptotic notations. I feel like I'm in over my head. I read the explanations in the text book, and Khan Academy. But when I try to do proofs, I can't grasp anything.

I'm trying to prove that If f (n) = ω(g(n)), then f (n) is not in O(g(n)) or o(g(n)).

I know that they don't intersect, as ω proves the lower bound (not tight) and O and o prove upper bounds. But I have no idea how to set up a proof to solve this.

Any help would be appreciated.

  • 1
    $\begingroup$ In these cases the proofs are almost always just manipulations of the definitions. You want to prove an implication (which we observe by the if-then style of the statement). So first let $f\in \omega(g)$ and write out exactly what this means. Then show that $f\notin O(g)$ and $f\notin o(g)$ hint: one of these implies the other $\endgroup$
    – awillia91
    Commented Sep 5, 2023 at 17:02

1 Answer 1


With a simplified notation, $\omega$ holds if $\forall\,c:f>c\,g$, while $O$ holds if $\exists\,c: f\le c\,g$.

These are obviously contradictory statements.


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