  Different mathematical methods have been applied to obtain the analytic
result for the massless triangle Feynman diagram yielding a sum of four
linearly independent hypergeometric functions $F_4$. In this paper I work out
the diagram and show that that result, though mathematically sound, is not
physically correct, because it misses a fundamental physical constraint imposed
by the conservation of momentum, which should reduce by one the total number of
linearly independent (l.i.) functions $F_4$ in the overall solution. Taking
into account that the momenta flowing along the three legs of the diagram are
constrained by momentum conservation, the number of overall l.i. functions that
enter the most general solution must reduce accordingly.
  To determine the exact structure and content of the analytic solution for the
three-point function, I use the analogy that exists between Feynman diagrams
and electric circuit networks, in which the electric current flowing in the
network plays the role of the momentum flowing in the lines of a Feynman
diagram. This analogy is employed to define exactly which three out of the four
hypergeometric functions are relevant to the analytic solution for the Feynman
diagram. The analogy is built based on the equivalence between electric
resistance circuit networks of type "Y" and "Delta" in which flows a conserved
current. The equivalence is established via the theorem of minimum energy
dissipation within circuits having these structures.
