Algebraic exceptional divisor
= Algebraic exceptional divisor
{title2=$E$}
The divisor contracted by a <blowup of an algebraic variety> to its centre. For the blowup of a smooth point on an $n$-dimensional smooth variety it is $\mathbb P^{n-1}$. Being a closed projective subvariety of positive dimension, it can obstruct affineness of a fibre containing it.