QEPCAD B~2 is a system for computing with semi-algebraic sets. a semi-algebraic set is a subset of R~n that can be defined as the set of points satisfying a boolean formula combining polynomial equalities and inequalities in the variables x_1,...,x_n. So, for example, the upper-right quadrant of the unit disk is a semi-algebraic set, since it has the defining formula[see pdf for formula x_1~2 + x_2~2 ≤ 1 Λ x_1 ≥ 0 Λ x_2 ≥ 0.
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