  The top quark antiquark production system in the dilepton decay channel is
described by a set of equations which is nonlinear in the unknown neutrino
momenta. Its most precise and least time consuming solution is of major
importance for measurements of top quark properties like the top quark mass and
$t\bar{t}$ spin correlations. The initial system of equations can be
transformed into two polynomial equations with two unknowns by means of
elementary algebraic operations. These two polynomials of multidegree two can
be reduced to one univariate polynomial of degree four by means of resultants.
The obtained quartic equation is solved analytically.
