d_1^2) \nonumber \\
\label{ModelSecondG6}
      |c| & = & \frac{1}{2} \sqrt{d_1^2 + d_2^2 - 
2d_1d_2\cos\theta} \\ 
x^2 + z^2 & = & \frac{1}{16} \, (d_1^2 + d_2^2 + 2
d_1d_2\cos\theta) - \frac{1}{4} \, |b|^2 \; . \nonumber\end{aligned}$$ In this case the $y-\,$coordinate is not constrained by the configuration of topological images, since the only orthogonal transformation involved in the calculations has the $y-\,$axis as its axis of rotation.

Numerical Examples {#Examples}
==================

Let us now apply the results obtained in the previous section to the proposed multiple images of Roukema and Edge [@RE97], in a FL universe whose matter components are pressureless dust and a cosmological constant. The models presented below are small universes with compactification scales much smaller than the horizon radius, so they may seem to be in conflict with constraints on the topology coming from observations of the CMBR. However, it must be recalled that all current constraints for flat universes hold exclusively for models with (i) toroidal spatial sections [@Torus; @Inoue], or (ii) any flat (compact and orientable) spatial section, but in cosmological models without a dark energy component, and moreover, with the observer located on the axis of rotation of a screw motion of the corresponding 