  The Fermi-liquid-like (FL) resistivity recently observed in clean HgBa2CuO4
below the pseudogap temperature was related to carriers at the nodal points on
the Fermi surface [4]. We show that this necessitates important implications
for the electronic spectrum of underdoped (UD) cuprates in whole. Photoemission
experiments picture the spectrum as of metallic arcs separated from each other
by regions with large energy gaps. We solved the kinetic equation in such model
rigorously. The Fermi arcs carriers contribute to FL resistivity, if scattering
between the opposite nodal points admits the Umklapp processes. The Hall
coefficient defines the effective number of carriers on arcs and has the
positive sign. For clean materials the expression is applicable only at weak
magnetic fields. We discuss the Fermi arcs concept further in light of recent
experimental findings and argue that the idea of reconstructed FS in UD
cuprates is not consistent with the FL-like resistivity.
