98% of people can't solve this
% *	+	=3
O - % -	=0
= z y| =^/#w ^ = Pn(R)
H>'l%,','^) has a ring structure
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":•(-, Z?) : C -? Set is contravariant ^(-4. Z?) = {(p : A —> i3|<p is a morphism}
given that	is the derived functor of *;• and sequence
0 —t i(C-y(H,;	—> H';w) —t	—+ 0.
is exact