%0 Journal Article %A Gamboa Mutuberria, José Manuel %A Fernando Galván, José Francisco %T On The Irreducible Components Of A Semialgebraic Set %D 2012 %@ 0129-167X %U https://hdl.handle.net/20.500.14352/42179 %X In this work we define a semialgebraic set S Rn to be irreducible if the noetherian ring of Nash functions on S is an integral domain. Keeping this notion we develop a satisfactory theory of irreducible components of semialgebraic sets, and we use it fruitfully to approach four classical problems in Real Geometry for the ring : Substitution Theorem, Positivstellens¨atze, 17th Hilbert Problem and real Nullstellensatz, whose solution was known just in case S = M is an affine Nash manifold. In fact, wegive full characterizations of the families of semialgebraic sets for which these classical results are true. %~