def write_rule(self, a, b, **attrs):
        if self.reverse:
            a, b = b, a
        "a -> b [a1=x,a2=y];"
        with self.rule():
            self.write('%s -> %s' % (self._nodename(a), self._nodename(b)))
            self._delattr(attrs, 'weight', 1)
            self._delattr(attrs, 'minlen', 1)
            self.write_attributes(attrs)
a -> b [a1=x,a2=y];