Been struggling to differentiate these two concepts. Is there an intuitive/graphical way to understand the difference between strict quasi-concave and quasi-concave functions? I understand the difference between concave and quasi-concave, but not between the strict and the normal version of quasi-concave.
I am aware of the difference in their formal definition where for quasi-concave it is
Definition (Quasi-concave). Let $f: \mathbb{R}^{n}\rightarrow \mathbb{R}$. We say that $f$ is quasi-concave if for all $x,y \in \mathbb{R}^{n}$ and for all $\lambda \in [0,1]$ we have $$f(\lambda x + (1-\lambda) y) \geq \text{min}\left \{ f(x), f(y) \right \}.$$ And a function is strict quasi-concave if $$f(\lambda x + (1-\lambda) y) > \text{min}\left \{ f(x), f(y) \right \}.$$
Aside from the differences in the $\geq$ and $>$ signs, am hoping to understand them visually/intuitively. Any help will be much appreciated.