The WHERE and COST clauses in quantified patterns, such as reachability patterns or shortest and cheapest path patterns, are limited to referencing a single variable only.

The following are examples of queries that are not supported because the WHERE or COST clauses reference two variables e and x instead of zero or one:

... PATH p AS (n) –[e]-> (m) WHERE e.prop > m.prop ...
... SHORTEST ( (n) (-[e]-> (x) WHERE e.prop + x.prop > 10)* (m) ) ...
... CHEAPEST ( (n) (-[e]-> (x) COST e.prop + x.prop )* (m) ) ...

The following query is supported because the subquery only references a single variable a from the outer scope, while the variable c does not count since it is newly introduced in the subquery:

... PATH p AS (a) -> (b)
      WHERE EXISTS ( SELECT * FROM MATCH (a) -> (c) ) ...