On combinatorics of quiver component formulas

Buch and Fulton conjectured the nonnegativity of the quiver coefficients appearing in their formula for a quiver variety. Knutson, Miller and Shimozono proved this conjecture as an immediate consequence of their component formula''. We present an alternative proof of the component formula by substituting combinatorics for Grobner degeneration. We relate the component formula to the work of Buch, Kresch, Tamvakis and the author where a splitting’’ formula for Schubert polynomials in terms of quiver coefficients was obtained. We prove analogues of this latter result for the type BCD-Schubert polynomials of Billey and Haiman.