We analyse the role of new weak and strong commensurability conditions on efficiency measures especially productivity measurement. If fails, then a index (indicator) may exhibit homogeneity bias yielding inconsistent contradictory results. In particular, we show that Luenberger indicator is sensitive to proportional changes in input-output quantities, while Malmquist not affected by such change...

I discuss a topological relation of the conduction property of a many-particle system on a periodic lattice at zero temperature to the energy spectrum. When the particle number per unit cell is an irreducible fraction p/q, an insulator must have q low-lying states of energy O(1/L) in one dimension and of energy O(1) in two dimensions, where L is the linear system size.

Theorem. For each arithmetic Fuchsian group Γ, there exists an infinite order elliptic element e such that e(ax(Γ)) = ax(Γ). Recall that a Fuchsian group is a discrete subgroup of PSL2(R) ∼= isom(H). We denote by ax(Γ) the set of axes of hyperbolic elements of the Fuchsian group Γ. The proof follows easily from known properties of arithmetic Fuchsian groups. Recall that an arithmetic Fuchsian g...