“…The problems (9)- (11) and 12- (16) are equivalent in the following sense. If the function w(t, x) is a classical solution to (9)- (11), then system of pairs (λ r (x), w r (t, x)), where λ r (x) = w(t r−1 , x) and w r (t, x) = w(t, x) − w(t r−1 , x), and (t, x) ∈ Ω r , and r = 1, m + 1 is a solution to problem (12)- (16). Conversely, if the system of pairs (λ * r (x), w * r (t, x)), (t, x) ∈ Ω r , and r = 1, m + 1, is a solution to (12)- (16), then the function w * (t, x) defined by the equalities w * (t, x) = λ * r (x) + w * r (t, x) for all (t, x) ∈ Ω r , and r = 1, m + 1, is a classical solution to problem (9)- (11).…”