|   | 1 |  initial version  | 
Not sure I understand the question. Maybe this helps a little.
Names are slightly changed with respect to the question.
Define two vectors and two symbolic variables:
sage: A = vector(var('x', n=3, latex_name='x'))
sage: B = vector(var('y', n=4, latex_name=r'\epsilon'))
sage: b = SR.var('b', latex_name='b')
sage: z = SR.var('z', latex_name='z')
Produce two new vectors combining the above:
sage: U = vector(SR, len(A) + len(B) + 1, A.list() + B.list() + [b])
sage: U
(x0, x1, x2, y0, y1, y2, y3, b)
sage: V = vector(SR, len(B) + 1, B.list() + [z])
sage: V
(y0, y1, y2, y3, z)
 Copyright Sage, 2010. Some rights reserved under creative commons license. Content on this site is licensed under a Creative Commons Attribution Share Alike 3.0 license.
 
                
                Copyright Sage, 2010. Some rights reserved under creative commons license. Content on this site is licensed under a Creative Commons Attribution Share Alike 3.0 license.