It is proved that if an entire function f: a", -> a", satisfies an equation of the form alpha (1)(x)beta (1)(y) + alpha (2)(x)beta (2)(y) + alpha (3)(x)beta (3)(y), x,y a C, for some alpha (j) , beta (j) : a", -> a", and there exist no and Ee for which , then f(z) = exp(Az (2) + Bz + C) a (TM) sigma (I")(z - z (1)) a (TM) sigma (I")(z - z (2)), where I" is a lattice in a",; sigma (I") is the Weierstrass sigma-function associated with I"; A,B,C, z (1), z (2) a a",; and .