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## 2. MAIN RESULT 

Problem 1 can be reduced to an inverse source problem. For this aim, let v ( p ) and v ( q ) be two solutions of (1.1)–(1.3) with the coefficients p and q respectively. Then the difference u = v ( p ) − v ( q ) satisfies 

<img src='content_image/306401.jpg'>

with f ( x, y ) = p ( x, y ) − q ( x, y ) and R = v ( q )( x, y, t ) . 

We consider the following inverse source problem: 

Problem 2 Let p, R be given suitably. Then determine f ( x, y ) , ( x, y ) ∈ D × G by the extra data ∂$_{ν}$u | $_{Σ}$. 

Here we do not assume the uniqueness of v ( p ) and v ( q ) but their existence. We have the following result for Problem 2. 

Theorem 1 Let p ∈ L $^{∞}$( D × {| y | < 2 L } ) and u satisfy (2.1)–(2.3) in D ×{| y | < 2 L } × ( − T, T ) . 

We assume that 

<img src='content_image/306402.jpg'>

