Definition of A++ in EBNF-Notation

$\displaystyle \flq expression\frq\$	$\displaystyle ::=$	$\displaystyle \flq abstraction\frq\ \vert$	(1)
		$\displaystyle \flq reference\frq\ \vert$
		$\displaystyle \flq synthesis\frq\$
$\displaystyle \flq abstraction\frq\$	$\displaystyle ::=$	$\displaystyle '(' \: define \: \flq variable\frq\ \: \flq expression\frq\ \: ')' \: \vert$	(2)
		$\displaystyle '(lambda (' \: \{ \flq variable \frq\ \} \: ')'$
		$\displaystyle \flq expression\frq\ \: \{ \: \flq expression\frq\ \} \: ')'$
$\displaystyle \flq reference\frq\$	$\displaystyle ::=$	$\displaystyle \flq variable\frq\$	(3)
$\displaystyle \flq synthesis\frq\$	$\displaystyle ::=$	$\displaystyle '(' \: \flq expression\frq\ \: \{ \flq expression\frq\ \} \: ')'$	(4)
$\displaystyle \flq variable\frq\$	$\displaystyle ::=$	$\displaystyle \flq symbol\frq\$	(5)