Denote by PSelf Ω (resp., Self Ω) the partial (resp., full) transformation monoid over a set Ω, and by SubV (resp., EndV ) the collection of all subspaces (resp., endomorphisms) of a vector space V . We prove various results that imply the following: (1) If cardΩ > 2, then Self Ω has a semigroup embedding into the dual of Self Γ iff card Γ > 2 . In particular, if Ω has at least two elements, th...

The notion of ring endomorphisms having large images is introduced. Among others, injectivity and surjectivity of such endomorphisms are studied. It is proved, in particular, that an endomorphism σ of a prime one-sided noetherian ringR is injective whenever the image σ(R) contains an essential left ideal L of R. If additionally σ(L) = L, then σ is an automorphism of R. Examples showing that the...

Let G0 be a connected unipotent group over a finite field Fq, and let G = G0 ⊗Fq Fq, equipped with the Frobenius endomorphism Frq : G −→ G. For every character sheaf M on G such that Frq M ∼= M , we prove that M comes from an irreducible perverse sheaf M0 on G0 such that M0 is pure of weight 0 (as an `-adic complex) and for each integer n ≥ 1 the “trace of Frobenius” function tM0⊗FqFqn on G0(Fq...