A Proposal to Extend Duality in String Theory in. VIII Taller de la División de Gravitación y Física Matemática, Preprinted
The so calledWick duality of General Relativity in 2+1 dimensions with a cosmological constant is extended to the low energy effective action of bosonic string theory in 2+1 dimensions. Next we compose it with timelike T duality. In order to read the effects of the composition of both dualities we use the BTZ solution of 2+1 gravity as our working example. Finally I suggest that this constitutes an exact symmetry of String Theory.