  All the causally regular geometries obtained from (2+1)-anti-de Sitter space
by identifications by isometries of the form $P \rightarrow (\exp \pi\xi) P$,
where $\xi$ is a self-dual Killing vector of $so(2,2)$, are explicitely
constructed. Their remarkable properties (Killing vectors, Killing spinors) are
listed. These solutions of Einstein gravity with negative cosmological constant
are also invariant under the string duality transformation applied to the
angular translational symmetry $\phi \rightarrow \phi+a$ The analysis is made
particularly convenient through the construction of {\em global} coordinates
adapted to the identifications.}
