private static function rule_signature( $lhs, array $rhs ){
		$a[] = $lhs;
		foreach( $rhs as $t ){
			$a[] = $t;
		}
		return implode( '.', $a );
	}
private static function rule_signature( $lhs, array $rhs ){
		$a[] = $lhs;
		foreach( $rhs as $t ){
			$a[] = $t;
		}
		return implode( '.', $a );
	}
private static function rule_signature ( $ lhs , array $ rhs ) { $ a [ ] = $ lhs ; foreach ( $ rhs as $ t ) { $ a [ ] = $ t ; } return implode ( '.' , $ a ) ; }
Create a signature to identify a rule uniquely
@param mixed scalar non-terminal symbol
@param array list of symbols in right hand side
@return string
Create a signature to identify a rule uniquely