Theory Versus Observations.

As discussed in Chapter 5, the fundamental problem of the EOS of neutronstar cores cannot be solved on purely theoretical basis: there is no strict theory but many theoretical models instead. Therefore, one can try to select (constrain) the true model using observations. In the present Chapter we will describe some results of this activity. The methods to constrain the EOS are numerous. The activity started just from the discovery of neutron stars in 1967 (Chapter 1). The results obtained by the time of this writing (2006) are a tremendous challenge of observational astrophysics, but look like a failure in their essence: the EOS has been only weakly constrained by observations. [ABSTRACT FROM AUTHOR]