  We study the logarithmic and ratio asymptotic of linear forms constructed
from a Nikishin system which satisfy orthogonality conditions with respect to a
system of measures generated from another Nikishin system. This construction
combines type I and type II multiple orthogonal polynomials. The logarithmic
asymptotic of the linear forms is expressed in terms of the extremal solution
of an associated vector valued equilibrium problem for the logarithmic
potential. The ratio asymptotic is described by means of a conformal
representation of an appropriate Riemann surface of genus zero onto the
extended complex plane.
