Hi,
I am busy to connect by a script two sets of vertices (connected by edges) and I encounter one big problem;
Suppose I have two ‘cycles’ (say two distinct circles lying in 3D) with equal number of vertices (and edges, naturally).
x1–x2–x3–x1 and
y1–y2–y3–y1 (in Python a list of vertex indices (first and last identical index make it a cycle).
Now I want to make face selecting e.g. x1 x2 y1 y2,and x2 x3 y2 y3
If I chose x1 x2 y1 y3 and x2 x3 y3 y2
the result will be totally different.
This means I have to know if the cycles are recorded clock-wise or anti-clock-wise
so to say a sort of orientation.
How to find out with the help of the corresponding 3D-vectors?
Any hint is welcome 
Here a picture of difference in orientation 
:Edit:
In principle the cross product of vectors may be used to decide …
E.g. take two vectors of either cycle and project them (z -coordinate = 0) onto x-y-space.
Then the third coordinate of the cross product decides if the ‘direction’ is equal …( + + or - - = equal, + - or - + unequal)
No decision is possible with this projection, than there are two other projections possible …
Maybe there are other ‘strange’ constallations…(I do not mind at this moment)