  The 4-loop sunrise graph with two massless lines, two lines of equal mass M
and a line of mass m, for external invariant timelike and equal to m^2 is
considered. We write differential equations in x=m/M for the Master Integrals
of the problem, which we Laurent-expand in the regularizing continuous
dimension d around d=4, and then solve exactly in x up to order (d-4)^3
included; the result is expressed in terms of Harmonic PolyLogarithms of
argument x and maximum weight 7. As a by product, we obtain the x=1 value,
expected to be relevant in QED 4-loop static quantities like the electron
(g-2). The analytic results were checked by an independent precise numerical
calculation
