A user could attempt to use a noun list with more than one entry (a "multi list") where a single noun is required. This is a semantic error rather than a grammatical error, so we define a grammar rule for it (despite the obvious clash with the singleNoun name). However, we use the BadListProduction for this match object - this ensures that we we score it lower than a version with out a list, and that if we make it to the resolution stage, we'll display a suitable error message.

grammar singleNoun(multiple) :   BadListProduction