  We consider an algebra of even-order square tensors and introduce a
stretching map which allows us to represent tensors as matrices. The stretching
map could be understood as a generalized matricization. It conserves algebraic
properties of the tensors. In the same time, we don't necessarily assume
injectivity of the stretching map. Dropping the injectivity condition allows us
to construct examples of stretching maps with additional symmetry properties.
Furthermore, the noninjectivity leads to the averaging of the tensor and
possibly could be used to compress the data.
