anchor.diff:  --
   This CIP limits the scope of `EXISTS` to existential subqueries and removes the syntax for property existence check.
   This check is enabled by `IS NOT NULL`.
  +It changes the syntax of existence constraints to be aligned with that removal.
   --
   
   toc::[]
  
positive.code: To clear out this confusion, this CIP proposes to remove the syntax of `EXISTS` for property existence checks and use only `IS NOT NULL` for this purpose.
  `IS NOT NULL` does not look like a function call and therefore it is unlikely that someone would expect it to behave like one.
  
  == Proposal
  
  This CIP proposes to redefine the syntax for `EXISTS`, previously defined in <<CIP2015-05-13-EXISTS.adoc,CIP2015-05-13>>.
  It removes  the syntax of `EXISTS` for property existence checks.
  
  === Syntax
  
  [source, ebnf]
  ----
  expression = <current definition of expression>
  
negative.code: == Caveats to this proposal
  
  * The idiomatic syntax for property existence checks is removed.
  * The syntax for creating and dropping node and relationship property existence constraints needs to be changed as well, to be aligned with the other syntax changes.
  