  The Standard Model (SM) with one right-handed neutrino per generation is
revisited with presymmetry being the global $U(1)_{B-L}$ symmetry of an
electroweak theory of leptons and quarks with initially postulated symmetric
fractional charges. The cancellation of gauge anomalies and the
non-perturbative normalization of lepton charges proceed through the mixing of
local and topological charges, the global $B-L$ measuring the induced charge
associated with a unit of topological charge, and the mathematical replacement
of the original fractional charges with the experimentally observed ones. The
$U(1)_{B-L}$ symmetry of the SM with Dirac neutrinos is seen as a residual
presymmetry. High-scale and low-scale seesaw mechanisms proposed to explain the
mass of neutrinos are examined from the perspective of presymmetry, be they of
Majorana or pseudo-Dirac type. We find that the tiny mass splitting in
pseudo-Dirac neutrinos and the mass of heavy neutrinos ride on the opposite
ends of the seesaw. We show that pseudo-Dirac neutrinos contain extra sterile
neutrinos with imprints of presymmetry and for heavy ones we get constraints
favoring the low-scale linear seesaw over the inverse variant.
