  Symmetric Grothendieck polynomials are analogues of Schur polynomials in the
K-theory of Grassmannians. We build dual families of symmetric Grothendieck
polynomials using Schur operators. With this approach we prove skew Cauchy
identity and then derive various applications: skew Pieri rules, dual
filtrations of Young's lattice, generating series and enumerative identities.
We also give a new explanation of the finite expansion property for products of
Grothendieck polynomials.
