anchor.diff:  * Are side effect-free, i.e. <FullExistentialSubquery> shall not contain any <UpdatingClause> or other sources of side effects
   * Can contain variables and parameters from the outer queries
   
  -https://raw.githack.com/openCypher/openCypher/master/tools/grammar-production-links/grammarLink.html?p=RelationshipsPattern[<RelationshipsPattern>] shall not introduce new variables.
  +https://raw.githack.com/openCypher/openCypher/master/tools/grammar-production-links/grammarLink.html?p=PatternPredicate[<PatternPredicate>] shall not introduce new variables.
   
   Both forms of https://raw.githack.com/openCypher/openCypher/master/tools/grammar-production-links/grammarLink.html?p=ExistentialSubquery[<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 an <ExistentialSubquery> are not available outside the subquery context.
   
  -https://raw.githack.com/openCypher/openCypher/master/tools/grammar-production-links/grammarLink.html?p=RelationshipsPattern[<RelationshipsPattern>] and <SimpleExistentialSubquery> are syntactically simpler and semantically less powerful forms of <FullExistentialSubquery>.
  -The semantics of https://raw.githack.com/openCypher/openCypher/master/tools/grammar-production-links/grammarLink.html?p=RelationshipsPattern[<RelationshipsPattern>] and <SimpleExistentialSubquery> can be defined as syntax transformations to <FullExistentialSubquery>.
  +https://raw.githack.com/openCypher/openCypher/master/tools/grammar-production-links/grammarLink.html?p=PatternPredicate[<PatternPredicate>] and <SimpleExistentialSubquery> are syntactically simpler and semantically less powerful forms of <FullExistentialSubquery>.
  +The semantics of https://raw.githack.com/openCypher/openCypher/master/tools/grammar-production-links/grammarLink.html?p=PatternPredicate[<PatternPredicate>] and <SimpleExistentialSubquery> can be defined as syntax transformations to <FullExistentialSubquery>.
   
   ==== <RelationshipsPattern>
   
  -A https://raw.githack.com/openCypher/openCypher/master/tools/grammar-production-links/grammarLink.html?p=RelationshipsPattern[<RelationshipsPattern>] _RP_ is effectively replaced by the expression
  -
  -`EXISTS { MATCH _RP_ RETURN 1 }`
  +A https://raw.githack.com/openCypher/openCypher/master/tools/grammar-production-links/grammarLink.html?p=PatternPredicate[<PatternPredicate>] _PP_ is effectively replaced by the expression
  +
  +`EXISTS { MATCH _PP_ RETURN 1 }`
   
   ==== <SimpleExistentialSubquery>
   
  
positive.code: 
  === Semantics
  
  https://raw.githack.com/openCypher/openCypher/master/tools/grammar-production-links/grammarLink.html?p=RelationshipsPattern[<RelationshipsPattern>], <SimpleExistentialSubquery>, and <FullExistentialSubquery> accomplish the same task: checking whether the result of a subquery is not empty.
  
  All three forms,
  
  
negative.code: 
  This CIP proposes:
  
  * Refer to a https://raw.githack.com/openCypher/openCypher/master/tools/grammar-production-links/grammarLink.html?p=RelationshipsPattern[<RelationshipsPattern>] appearing as an https://raw.githack.com/openCypher/openCypher/master/tools/grammar-production-links/grammarLink.html?p=Atom[<Atom>] as a https://raw.githack.com/openCypher/openCypher/master/tools/grammar-production-links/grammarLink.html?p=PatternPredicate[<PatternPredicate>] for better distinguishing it from a https://raw.githack.com/openCypher/openCypher/master/tools/grammar-production-links/grammarLink.html?p=RelationshipsPattern[<RelationshipsPattern>] appearing in a https://raw.githack.com/openCypher/openCypher/master/tools/grammar-production-links/grammarLink.html?p=PatternComprehension[<PatternComprehension>]
  * Restricting https://raw.githack.com/openCypher/openCypher/master/tools/grammar-production-links/grammarLink.html?p=PatternPredicate[<PatternPredicate>] to predicate contexts and boolean evaluation, when used in expression contexts
  * Adding two forms of existential subqueries denoted with `EXISTS { ... }`:
  ** Full existential subquery based on a https://raw.githack.com/openCypher/openCypher/master/tools/grammar-production-links/grammarLink.html?p=RegularQuery[<RegularQuery>]
  ** Simple existential subquery based on a single https://raw.githack.com/openCypher/openCypher/master/tools/grammar-production-links/grammarLink.html?p=Pattern[<Pattern>] and an optional https://raw.githack.com/openCypher/openCypher/master/tools/grammar-production-links/grammarLink.html?p=Where[<Where>] clause
  