sentences:  Krivine–Stengle Positivstellensatz
  
  In real algebraic geometry, Krivine–Stengle (German for "positive-locus-theorem") characterizes polynomials that are positive on a semialgebraic set, which is defined by systems of inequalities of polynomials with real coefficients, or more generally, coefficients from any real closed field.It can be thought of as an real analogue of Hilbert's Nullstellensatz, (which concern complex zeros of polynomial ideals), and this is this analogy that is at the origin of its name.