  It is shown that the appearance of a fixed-point singularity in the kernel of
the two-electron Cooper problem is responsible for the formation of the Cooper
pair for an arbitrarily weak attractive interaction between two electrons. This
singularity is absent in the problem of three and few superconducting electrons
at zero temperature on the full Fermi sea. Consequently, such three- and
few-electron systems on the full Fermi sea do not form Cooper-type bound states
for an arbitrarily weak attractive pair interaction.
