Close the SPARQL gap by providing support for modeling MINUS operator. This operator acts like a "subtractor" of data from the left query member, basing its logic on the following assumption: "if this row outer-joins with the target row on common variable bindings then it is compatible, so...it must be discarded".

Provide a MinusWithNext() operator to RDFPattern, RDFPatternGroup and RDFSelectQuery.

Update RDFQueryPrinter to properly handle the presence of this first-class algebra citizen, which may interact and nest with active UNION and OPTIONAL operators.