Search for b -> u transitions in B-->[K+pi(-)pi(0)](D)K-

We search for decays of a B meson into a neutral D meson and a charged kaon, with the D meson decaying into a charged kaon, a charged pion, and a neutral pion. This final state can be reached through the b -> c transition B-->(DK-)-K-0 followed by the doubly Cabibbo-suppressed D-0 -> K+pi(-)pi(0), or the b -> u transition B-->(D) over tilde K-0(-) followed by the Cabibbo-favored (D) over bar (0)-> K+pi(-)pi(0). The interference of these two amplitudes is sensitive to the angle gamma of the unitarity triangle. We present results based on 226x10(6) e(+)e(-)->Upsilon(4S)-> B (B) over bar events collected with the BABAR detector at SLAC. We find no significant evidence for these decays and we set a limit R-ADS equivalent to Gamma([K+ pi(-) pi(0)](D)K-) +Gamma([K- pi(+) pi(0)](D)K+)/Gamma([K+ pi(-) pi(0)](D)K+) +Gamma(K- pi(+) pi(0)](D)K-) < 0.039 at 95% confidence level, which we translate with a Bayesian approach into r(B)equivalent to|A(B-->(D) over bar K-0(-))/A(B-->(DK-)-K-0)|< 0.19 at 95% confidence level.