  I begin from a particular field of generalised Puiseux series and investigate
a class of nonlinear differential equations in the field. It is appeared that
the main part of differential equation determines solvability and positions of
resonance i.e. the appearance of a free constant in solutions. Secondly, for
any singular differential equation in a differential field of the form
$Q(y)\dot y=P(y)$, $P,Q$ polynomials. Then the greatest Picard-Vessiot
extension exists. It is shown that the arising set of solutions is obtained
from algebraic equations labelled by constants. Sufficient conditions for the
PV extension being extended liouvillian are delivered.
