anchor.diff:    NAME '(' expression (',' expression)* ')' lambdaExpression?;
   
   comprehensionExpression returns [Comprehension comprehension]:
  -  (pathExpression | FOR enumeratorDeclaration (',' enumeratorDeclaration)*)
  +  (pathExpression |
  +   FOR enumeratorDeclaration (',' enumeratorDeclaration)*)
     queryStatement+;
   
   enumeratorDeclaration returns [Enumerator enumerator]:
  
positive.code: import Literals, Types;
  
  expression returns [Expression expr]
    : literalExpression | pathExpression
    | lambdaExpression  | invocationExpression
    | comprehensionExpression
  
    // Grouping
  
negative.code:   | expression operator=IMPLIES expression
  
    // Conditional Expressions:
    | IF cond=expression
      THEN then=expression ELSE else_=expression
    | then=expression conj=(GIVEN | UNLESS) cond=expression
    | then=expression (ORQ | XORQ) else_=expression;
  
  