  This article contains a proof of the basic lemma. This lemma, discovered by
Beilinson, yields a motivic proof of the Andreotti-Frankel theorem for affine
varieties. Next, it is shown that the category of Cohomologically Constructible
Sheaves (as it is referred to in the Riemann-Hilbert correspondence) coincides
with the derived category of bounded complexes of constructible sheaves. It is
also shown that higher direct images and the sheaf-Ext groups are effaceable in
the category of constructible sheaves.
