[see also: basic, critical, crucial, essential, main
The key observation is that if......
The key part is to show that the submanifolds Uk fit together to form a complex submanifold.
A key step in obtaining (6) is Hölder's inequality.
We shall prove this theorem shortly, but first we need a key lemma.
It supplies the key to the proof of Theorem 2.
The following lemma is the key to extending Wagner's results.