# Nefness of h-e$h-e$ in the blowup of P^n$\mathbb{P}^n$
Let S $S$ be the blow up of P^n $\mathbb{P}^n$ in a point P. $P$. Let h $h$ be the class of the pullback of an hyperplane of P^n $\mathbb{P}^n$ and e $e$ the class of the exceptional divisor. Why is the divisor l=h-e $l=h-e$ nef? Thank you very much!