Unique continuation and an inverse problem for hyperbolic equations across a general hypersurface

We consider a hyperbolic equation p(x,t)partial derivative(2)(t)u(x,t) = Delta u(x,t) + Sigma(n)(k=1) qk(x, t)partial derivative ku+ qn+l (x, t)partial derivative(t)u + r(x, t)u in R-n x R with p is an element of C-1 and q(1)...... q(n+l), r is an element of L-infinity. Let r be a part of the boundary of a domain and let v(x) be the inward unit normal vector to Gamma at x. Then we prove the conditional stability in the unique continuation near a point x(0) across Gamma if del P(x(0), t) (.) v(x(0)) < 0 and the radius of the osculating ball at x(0) is large for -del p(x(0),t) (.) v(x(0)). Next we prove the conditional stability in the inverse problem of determining a coefficient r(x) from Cauchy data on Gamma over a time interval. The key is a Carleman estimate in level sets of paraboloid shapes.