Set Nodes

[eraserwww]

Hello,

I have a python model. The demands enforce two adjacent RVEs to show identical deformations, while neither overlapping nor separation may occur. Considering two opposite point, A and B, and other set of opposite points, C and D, their displacements, ui, respecting the periodicity of the RVE can be written in terms of the average unit cell strain.
I can select nodes of the faces, but I can not give in set to after apply the BC´s. I'd have to select the one side and we apply the same conditions of parallelism, as shown in the script below:

# Number of nodes/elements
assy = Model.rootAssembly
nNodes=0
nElems=0
for Square1 in assy.instances.keys():
nn=len(assy.instances[Square1].nodes)
ne=len(assy.instances[Square1].elements)
nNodes = nNodes + nn
nElems = nElems + ne
print 'Number of nodes:', nNodes
print 'Number of elements:', nElems


# Select nodes from FaceX+ and set with "NodesFaceX+"
tol=1.0E-9
no=[]
for i in assy.instances[Square1].nodes:
if ((i.coordinates[0] < side+tol) and (i.coordinates[0] > side-tol)):
no.append(i)

How to transform this vector with the selected nodes in the set to apply parallelism between the faces of a cube.