anchor.diff:  
   Both forms of <ExistentialSubquery> (<SimpleExistentialSubquery> and <FullExistentialSubquery>) are allowed to introduce new variables.
   These variables necessarily shall have a name different from the names of all variables available from the outer queries.
  -Any variables introduced in a <ExistentialSubquery> are not available on the outside.
  +Any variables introduced in an <ExistentialSubquery> are not available on the outside.
   
   <RelationshipsPattern> and <SimpleExistentialSubquery> are syntactically simpler and semantically less powerful forms of <FullExistentialSubquery>.
  -Hence, the semantics of <RelationshipsPattern> and <SimpleExistentialSubquery> can be defined as syntax transformations to <FullExistentialSubquery>.
  -
  -==== `<RelationshipsPattern>`
  -
  -A `<RelationshipsPattern>` _RP_ is effectively replaced by the expression
  +The semantics of <RelationshipsPattern> and <SimpleExistentialSubquery> can be defined as syntax transformations to <FullExistentialSubquery>.
  +
  +==== <RelationshipsPattern>
  +
  +A <RelationshipsPattern> _RP_ is effectively replaced by the expression
   
   `EXISTS { MATCH _RP_ RETURN 1 }`
   
  -==== `<SimpleExistentialSubquery>`
  -
  -A `<SimpleExistentialSubquery>` _SES_ is effectively replaced by the expression
  +==== <SimpleExistentialSubquery>
  +
  +A <SimpleExistentialSubquery> _SES_ is effectively replaced by the expression
   
   `EXISTS { MATCH _SES_ RETURN 1 }`
   
  -==== `<FullExistentialSubquery>`
  +==== <FullExistentialSubquery>
   
   A <FullExistentialSubquery> _FES_ is effectively evaluated as follows:
   
  
positive.code: [abstract]
  .Abstract
  --
  This CIP introduces `EXISTS`, a function and a keyword for checking the existence of properties, simple patterns and full subqueries.
  --
  
  toc::[]
  
negative.code: Both are allowed as https://github.com/opencypher/openCypher/blob/master/grammar/basic-grammar.xml#L296[<Atom>]s of expressions.
  
  Note that a <RelationshipsPattern> appearing in an expression is evaluated to a list containing the matches of the pattern.
  In a predicate context this list gets coerced to a boolean (empty list -> [underline]#*_False_*#, non-empty list -> [underline]#*_True_*#), letting this <RelationshipsPattern> behave like a predicate although it actually is a list expression.
  As a result, <RelationshipsPattern>s appear to behave differently depending on the context in which they appear.
  Further, https://github.com/opencypher/openCypher/blob/master/grammar/basic-grammar.xml#L432[<PatternComprehension>] offer a more powerful and syntaxtically better separated means to   get lists of matches for a pattern within expressions.
  
  The understanding of subqueries in Cypher has evolved and Cypher gained a proper https://github.com/opencypher/openCypher/blob/master/grammar/basic-grammar.xml#L277[<NullOperatorExpression>] (`IS [ NOT ] NULL`), cf. https://github.com/opencypher/openCypher/blob/master/cip/1.accepted/CIP2018-10-29-EXISTS-and-IS-NOT-NULL.adoc[CIP2018-10-29 EXISTS and IS NOT NULL].
  Both developments and the issues around <RelationshipsPattern>s suggest the need for a refinement of the language constructs that allow testing of existence.
  
  == Proposal
  
  CIP proposes:
  
  * Restricting <RelationshipsPattern> to predicate contexts and boolean evaluation
  * Adding two forms of existential subqueries denoted with `EXISTS { ... }`:
  ** Full existential subquery based on a https://github.com/opencypher/openCypher/blob/master/grammar/cypher.xml#L76[<RegularQuery>]
  ** Simple existential subquery based on a single https://github.com/opencypher/openCypher/blob/master/grammar/basic-grammar.xml#L56[<Pattern>] and an optional https://github.com/opencypher/openCypher/blob/master/grammar/basic-grammar.xml#L47[<Where>] clause
  * Removing of `exists( n.prop )` in favor of the https://github.com/opencypher/openCypher/blob/master/grammar/basic-grammar.xml#L277[<NullOperatorExpression>], which is a restatement of what has been accepted with https://github.com/opencypher/openCypher/blob/master/cip/1.accepted/CIP2018-10-29-EXISTS-and-IS-NOT-NULL.adoc[CIP2018-10-29 EXISTS and IS NOT NULL]
  