anchor.diff:  Nonterminals
  -  Program
  -  Number
  -  PrimaryExpression
  -  SimpleExpression
  -  ParenthesizedExpression
  -  UnaryExpression
  -  ExponentialExpression
  -  MultiplicativeExpression
  -  AdditiveExpression
  -  Expression
  +  Grammar
  +  Statements
     Statement
     StatementEnding
     EmptyStatement
     ExpressionStatement
  -  Statements
  +  Expression
  +  AdditiveExpression
  +  MultiplicativeExpression
  +  ExponentialExpression
  +  UnaryExpression
  +  PrimaryExpression
  +  SimpleExpression
  +  ParenthesizedExpression
  +  Number
     .
     
   Terminals
  
positive.code: %% Expression Statement 
  ExpressionStatement -> Expression : '$1'.
  
  %% Programs
  
  Program -> Statements : '$1'.
  Statements -> '$empty' : [].
  Statements -> Statements Statement: '$1' ++ ['$2'].
negative.code: %  '{' '}' '&' '^' '||' '|' '||='
    .
  
  Rootsymbol Grammar.
  
  Grammar -> Statements : '$1'.
  Statements -> '$empty' : [].
  Statements -> Statements Statement: '$1' ++ ['$2'].
  
  %% Statements
  Statement -> EmptyStatement : '$1'.
  