Day of the World Tree, 57th of Spring, 525 M.E. (Deneb): Towards the end of the Heart Sutra, the Prajñā-Pāramitā mantra is invoked  It is introduced in the sutra as "the great miraculous manta, the great bright manta, the supreme mantra, the incomparable mantra which removes all suffering and is true not false." 

It is my least favorite part of the Heart Sutra. It's so insistent on the virtue of the mantra and tries so hard to sell it that I've always wanted to go on and ad lib, "the really fucking swell mantra, it really is the best mantra, the guarantee your money back mantra, you won't find a better mantra, goddamn I really love this mantra," etc.

Buddhism is generally humble about its virtues and encourages its followers to question and critically evaluate the teachings. So it's a bit surprising the way the Heart Sutra insists that the Prajñā-Pāramitā sutra ("gate, gate,  pāragate, pārasamgate, bodhi, svāhā") is so superior to any other. That last phrase ("and is true not false") is especially jarring in its stark duality for a religion that preaches non-duality ("these is no up, there is no down, these is no true and false").

In 1994, Gudo Nishijima translated those lines of the Heart Sutra as, "So remember: prajñā-pāramitā is a great and mystical spell; it is a great and luminous spell; it is the supreme spell; it is a spell in the unequaled state of equilibrium. It can clear away all suffering. It is real, not empty." A later (2007) version of his translation used the traditional term "mantra" instead of "spell." 

I like "real, not empty" much more than "true, not false," especially in the way that "emptiness," or shunyatā, is understood in Zen (impermanent, devoid of an independent existence). 

In his commentary on the Heart Sutra, Zen Master Dogen pointed out that the manifestation of prajñā (wisdom) is the arising of the myriad things (the real dharmas), while the real dharmas are themselves aspects of emptiness. Form is emptiness, and emptiness is form.

So one can assume that the Heart Sutra is saying that actual wisdom, prajñā, not the words of the Prajñā-Pāramitā mantra or even the practice of chanting, is the manifestation of reality (the myriad things) and the myriad things are all impermanent and empty of an independence existence. I can understand how translators might come up with "true, not false" from whatever the original words were, but I like "real, not empty" much more.

At this point, someone out there is wondering, "Sure, but the sutra is saying it's 'not empty' and you're saying 'all things are empty.' So which is it?" 

I'm saying that all things are empty and without all things there is no emptiness. Interdependence.