  Within an isospin- and momentum-dependent hadronic transport model it is
shown that the recent FOPI data on the $\pi^-/\pi^+$ ratio in central heavy-ion
collisions at SIS/GSI energies (Willy Reisdorf {\it et al.}, NPA {\bf 781}, 459
(2007)) provide circumstantial evidence suggesting a rather soft nuclear
symmetry energy \esym at $\rho\geq 2\rho_0$ compared to the
Akmal-Pandharipande-Ravenhall prediction. Some astrophysical implications and
the need for further experimental confirmations are discussed.
