m=(((1,2),(2,4)),((2,3),(5,6))) is a rank 3 tensor with dimension 2, a vector of matrices.
A tensor is a nested list.
An example Eigenmath http://eigenmath.net/ script with a rank 3 tensor is:
--Maxwell equations in tensor form.
--See the book Gravitation p. 81.
--
-- F + F + F =...