The various parts related to the definition of ORDER BY lack a clear definition of the kind of conditions they are dealing with:

• Section 18.2.5.1 ORDER BY just mentions some "list of order comparators" that is used for placing an OrderBy operator into the algebraic expression that is created, without saying what exactly such an "order comparator" is (and where the "order comparators" for the list come from).
• The "Definition: Evaluation of OrderBy" in Section 18.6 Evaluation Semantics simply assumes that the corresponding operator as an argument called "condition", without any further clarification.
• The definition of the OrderBy algebra operator also just mentions an argument called "condition". Moreover, in addition to not specifying what exactly such a condition is, the definition also does not specify clearly the meaning of this condition; the definition simply states that "the [result] sequence satisfies the ordering condition" but nowhere does the spec say what it means for a sequence of solution mappings to satisfy an ordering condition.