In the context of Lee Peng Yee’s problem sets, Number Theory moves beyond simple arithmetic into modular arithmetic and divisibility properties.
The Cox ring (or total coordinate ring) of a variety (X) is the multigraded ring [ \operatornameCox(X)=\bigoplus_[D]\in\operatornameCl(X) H^0(X,\mathcalO_X(D)), ] where (\operatornameCl(X)) is the divisor class group. For toric varieties it coincides with a polynomial ring, a fact that underpins many combinatorial constructions. pure maths lee peng yee pdf link