Solid with a crack and friction

We keep the notation of Section 1.4.4. Let us prove an auxiliary statement. 

This assertion is a consequence of the norm definition given in Section 1.4.2. Indeed, we can write 

For a given external force / = (/i,/2,/3) G L flc), we introduce the potential energy functional 

Theorem 1.31. There exists a unique solution u G K to the problem (1.161) such that 

This means that the following equations hold  

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