---
abstract: 'Suppose we have identified three clusters of galaxies as being topological copies of the same object. How does this information constrain the possible models for the shape of our Universe? It is shown here that, if our Universe has flat spatial sections, these multiple images can be accommodated within any of the six classes of compact orientable 3-dimensional flat space forms. Moreover, the discovery of two more triples of multiple images in the neighbourhood of the first one, would allow the determination of the topology of the Universe, and in most cases the determination of its size.'
author:
- |
    G.I. Gomero[^1],\
    \
    Instituto de Física Teórica,\
    Universidade Estadual Paulista,\
    Rua Pamplona, 145\
    São Paulo, SP 01405–900, Brazil
title: '**Determining the shape of the Universe using discrete sources**'
---

Introduction
============

The last two decades have seen a continuously increasing interest in studying cosmological models with multiply connected spatial sections (see [@Review] and references therein). Since observational cosmology is becoming an increasingly high precision science, it would be of wide interest to develop methods to systematically construct specific candidates for the shape of our Universe in order to analyse whether these models are consistent with observational data.

Since 