<Dl> <Dd> Q (x, ∂) φ (x) = ∑ (− 1) α ∂ α 1 ∂ α 2 ⋯ ∂ α n (a α 1, α 2,..., α n (x) φ (x)). (\ displaystyle Q (x, \ partial) \ varphi (x) = \ sum (- 1) ^ (\ alpha) \ partial ^ (\ alpha _ (1)) \ partial ^ (\ alpha _ (2)) \ cdots \ partial ^ (\ alpha _ (n)) \ left (a_ (\ alpha _ (1), \ alpha _ (2), \ dots, \ alpha _ (n)) (x) \ varphi (x) \ right).) </Dd> </Dl> <Dd> Q (x, ∂) φ (x) = ∑ (− 1) α ∂ α 1 ∂ α 2 ⋯ ∂ α n (a α 1, α 2,..., α n (x) φ (x)). (\ displaystyle Q (x, \ partial) \ varphi (x) = \ sum (- 1) ^ (\ alpha) \ partial ^ (\ alpha _ (1)) \ partial ^ (\ alpha _ (2)) \ cdots \ partial ^ (\ alpha _ (n)) \ left (a_ (\ alpha _ (1), \ alpha _ (2), \ dots, \ alpha _ (n)) (x) \ varphi (x) \ right).) </Dd> <Dl> <Dd> (− 1) α = (− 1) α 1 + α 2 + ⋯ + α n (\ displaystyle (- 1) ^ (\ alpha) = (- 1) ^ (\ alpha _ (1) + \ alpha _ (2) + \ cdots + \ alpha _ (n))) </Dd> </Dl> <Dd> (− 1) α = (− 1) α 1 + α 2 + ⋯ + α n (\ displaystyle (- 1) ^ (\ alpha) = (- 1) ^ (\ alpha _ (1) + \ alpha _ (2) + \ cdots + \ alpha _ (n))) </Dd>

What is the difference between a weak and strong solution