when m > 0. Writing (1) as a quasilinear symmetric hyperbolic system, it is known that a classical solution exists locally in time. provided that f, g are “small” and sufficiently smooth. The time interval [O. T] for which this classical solution exists depends on the size of the initial data. More precisely, if f = .@,, and g = &go where fO, go are fixed, the largest time T = T(E) for which the classical solution of (1) is assured by the Local Existence Theorem is of order l/~. For the one dimensional genuine nonliner wave equation. i.e. m = 0, n = 1 in (1) and cy= 1 in (2). Lax [l] has shown that this estimate is sharp. In this case when the genuine nonlinearity condition is violated. i.e. LY> 1, Klainerman and Majda [2] have shown that T(E) = 0( l/.?) and that this estimate is also sharp for E sufficiently small. In contrast to the one dimensional case, John has shown that in higher dimensions the existence time of classical solutions can be significantly improved. In fact, he proved for the case m = 0, (Y = 1, that T(E) = 0( l/s) for n = 4,5 [3] and recently T(E) = U( l/8) for
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