Assertion: `vec(A)xxvec(B)` is perpendicualr to both `vec(A)-vec(B)` as well as

Assertion: `vec(A)xxvec(B)` is perpendicualr to both `vec(A)-vec(B)` as well as `vec(A)-vec(B)` Reason: `vec(A)xxvec(B)` as well as `vec(A)-vec(B)` lie in the plane containing `vec(A)` and `vec(B)`, but `vec(A)xxvec(B)` lies perpendicular to the plane containing `vec(A)` and `vec(B)`.