This pair of works, entitled "Tesis y Antítesis del Espacio" (Thesis and Antithesis of Space), represents the turning point with which the sculptor abandons the natural reference, focusing on the relationship between volume and space.

Starting with an initial volume in the shape of a prism, which Mateos gradually perforates and empties, he realises that the hollow created, the empty space, becomes the protagonist. Thus, the hollow is also another volume, a negative volume. And from this duality arise the Thesis and Antithesis of space: the extracted volume and the void left in the initial prism.

Responding to this more rational approach, the texture of the formwork in this work does not have the same presence as in the rest of the series. We can observe, however, a different arrangement of the wood on the exterior faces, with a horizontal framework, as opposed to an oblique framework on the interior planes.

With this pair of works, the sculptor ends this series, which he therefore generically calls "Espaciales", but also concludes the expressionist stage in which his work has been framed until now. From now on his work will evolve towards constructivist areas.