Systematic smoothing of constrained interface profiles

We introduce a family of crossing constraints for defining an interface Hamiltonian that yield order-parameter profiles of any desired smoothness. The usual local crossing criterion is generalized to include integral constraints. Application to short-range critical wetting allows us to demonstrate that fundamental predictions from the local crossing criterion are robust under a change of constraint. Further, interface Hamiltonians derived from any member of the family are shown to reproduce exact results for order-parameter correlation functions.