A projective normal and $\mathbb{Q}$-factorial variety $X$ is said to be log Fano if there exists and effective divisor $D$ on $X$ such $-K\_X-D$ is ample and the pair $(X,D)$ is klt.


Now, let $f:X\dashrightarrow Y$ birational map which is an isomorphism in codimension one between two projective normal and $\mathbb{Q}$-factorial varieties. Assume that the strict transform of $-K\_X$ on $Y$ is nef and big. Can we conclude that then $X$ is log Fano? I know that this holds if the strict transform of $-K\_X$ on $Y$ is ample.


Thank you very much.



Weak Fano varieties and small transformations
You need to know that $Y$ as at worst klt singularities. In this case $Y$ is a weak Fano variety with klt singularities and then it is log Fano.


Now, you are done since a small $\mathbb{Q}$-factorial transfomation of a log Fano variety is log Fano.


