  The twist two contribution in the operator product expansion of phi_1(x_1)
phi_2(x_2) for a pair of globally conformal invariant, scalar fields of equal
scaling dimension d in four space-time dimensions is a field V_1(x_1,x_2) which
is harmonic in both variables. It is demonstrated that the Huygens bilocality
of V_1 can be equivalently characterized by a "single-pole property" concerning
the pole structure of the (rational) correlation functions involving the
product phi_1(x_1) phi_2(x_2). This property is established for the dimension
d=2 of phi_1, phi_2. As an application we prove that any system of GCI scalar
fields of conformal dimension 2 (in four space-time dimensions) can be
presented as a (possibly infinite) superposition of products of free massless
fields.
