For an affine Lie algebra ĝ, the coefficients of certain vertex operators that annihilate level k standard ĝ-modules are defining relations for modules. In this paper, we study a combinatorial structure leading terms these = 2 algebras type Cn(1) and main result is construction combinatorially parameterized among annihilating fields. It believed constructed will play key role in Gröbner-like ba...