In a graph $G=(V,E)$ of order $n$, what fraction of the $binom(n,4)$ \binom{n}{4}$ $4$-subsets of $V$ can induced induce the path of order four?
I looked at this question a 30 years ago and was never able to come up with a respectable upper bound. The question has reared it's its head again. The answer appears to be somewhere between $1/4$ and $1/3$, though that upper bound is almost certainly weak. Ideas?

