  In this note we prove a well-posedness result, without loss of derivatives,
for strictly hyperbolic wave operators having coefficients which are
Zygmund-continuous in the time variable and Lipschitz-continuous in the space
variables. The proof is based on Tarama's idea of introducing a lower order
corrector in the energy, in order to produce special algebraic cancellations
when computing its time derivative, combined with paradifferential calculus
with parameters, in order to handle the low regularity of the coefficients with
respect to $x$.
