In 1970, Stefan Bertalan together with Constantin Flondor laid the foundation for a new art group, Sigma group, when more young artists joined them, who they were all teaching at the Art High school in Timisoara (Doru Tulcan, Elisei Rusu, Ion Gaita and the mathematician Lucian Codreanu). A defining characteristic of this new group was the declared program of work, based on the principle of team and interdisciplinary work (mathematics, cybernetics, bionics, but also plastic structures). The first creation period of Sigma group (1970-1974) is characterised by projects made in common, visible also in the system of participation in exhibitions. One example of such a project was "The Informational Tower", conceived in 1970, mixing architecture and sculpture, exhibited information within a show of light and sound. But not only the public projects, as the geometric structure realized in 1971 for the hallway of the Students' House in Timisoara or the project of fountain which brought them an U.A.P. prize, have marked the important moments of the group's development; a new vision upon their subsequent evolution was to be marked by the action and the environment called "bloating structures" and realized at the Bastion Gallery in Timisoara, for the UNESCO Plastic Arts' Week. In the Bastion Gallery the rooms have been organized with bloating structures in the form of transparent tubes, onto which, during the opening, a dia and film projection took place. Thus, the spatial environment took the form of a happening with public assistance. In the same year, Bertalan, Flondor and Tulcan were invited to participate in the exhibition "Art and Energy" in Bucharest, where they created spatial installations which were separate but at the same time within a unitary ensemble that carried the unmistakable mark of the group. The last big common action of the group before they separated was "Multi-vision" (presented at the exhibition "Study 1", Timisoara, 1978), a spatial environment formed by a tri-dimensional structure made of coloured semi-transparent nets, spatially arranged in the form of a tetrahedron, onto which there was a projection of black and white and colour film for two cameras.
Source: Ileana Pintilie, "Spira mirabilis"