Expression of Negative Constraints

Negative constraints are used to limit the scope of acceptable FDs by the grammar and to force failure when certain FD configurations are met. The main tools in FUF for the expression of negative constraints are FSET and NONE. The main sources of confusion here are:

• FSET is too restrictive: you didn't plan on adding a feature, a new feature is not compatible with FSET.  

• FSET must include explicitly all the features, including CAT and CSET.

• NONE is used in the wrong place.