given a vector space V over a field K, a k-tensor is a k-variable function V x ... x V -> K which is linear in each argument.

그리고 텐서곱은 정의가 단순함
Let T and S be a k and l-tensor respectively. The tensor product T (x) S is a (k+l)-tensor defined by T(x)S(X, Y) = T(X)S(Y) where X = (u_1, ... ,u_k), Y = (v_1, ... , v_l) are k and l-ordered-tuple of vectors, respectively.
그냥 인자별로 그에 맞는 함수값 구해서 곱한거