Partial derivative - Wikipedia
https://en.wikipedia.org/wiki/Partial_derivativeSecond and higher order partial derivatives are defined analogously to the higher order derivatives of univariate functions. For the function the "own" second partial derivative with respect to x is simply the partial derivative of the partial derivative (both with respect to x): The cross partial derivative with respect to x and y is obtained by taking the partial derivative of f with respect to x, and then taking the partial derivative of the result with respect to y, to obtain
Cross product - Wikipedia
https://en.wikipedia.org/wiki/Cross_productThe cross product of two vectors a and b is defined only in three-dimensional space and is denoted by a × b.In physics and applied mathematics, the wedge notation a ∧ b is often used (in conjunction with the name vector product), although in pure mathematics such notation is usually reserved for just the exterior product, an abstraction of the vector product to n dimensions.