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[Václav Šmilauer <eudoxos@xxxxxxxx>]

> 1) case
>
> box -> id=0
> sphere -> id=1
>
> Interaction:
> id1=0 (box)
> id2=1 (sphere)
>
> 2) case (I switch ids, alias I change the sequence in which I append the 
> two bodies)
>
> sphere -> id=0
> box -> id=1
>
> Interaction:
> id1=1 (box) ---> why it is not id=0 as in the first case?
> id2=0 (sphere)
>
> My question is: how are assigned the ids of the contact once the 
> interaction is created?

Wow, you have such bright questions :-)

It really depends on the order in which the collider creates the 
interaction in the first place. Then, asymmetric geometry functors might 
ask to swap the ids (e.g. Ig2_Box_Sphere_ScGeom will always change the 
interaction so that Box is id1 and Sphere is id2) so that they are in 
the order they accept (this happens in InteractionDispatchers loop).

If you look for interaction, the order of ids is irrelevant, 
O.interactions[i,j]==O.interactions[j,i] should be always true.

Cheers, Vaclav