x1 is counterclockwise/left-turn-direction of[/to] x2 along/following track x3 [path] in frame of reference x4 (where the axis is within the region defined by the track as the boundary, as viewed from and defined by view(er) x4; see notes); x1 is locally to the left of x2, according to x4, constrained along x3; x1 is along a left turn from x2 along path x3, as viewed in frame x4.
mekso binary operator: left-handed vectorial cross product (ordered input), -a \times b = b \times a (if using right-hand convention - notice the negative sign/operator or order).