Peter Skilling is a special lecturer at Chulalongkorn University, Bangkok, and an honorary associate, Department of Indian SubContinental Studies, University of Sydney, Australia. Until his retirement in 2017, he was a professor of the French School of Asian Studies (EFEO) based in Bangkok. He was awarded an honorary doctorate in the humanities by Chulalongkorn University in 2020. He is an honorary member of the Siam Society, Bangkok, and in 2017 he was elected an honorary fellow of the Asiatic Society of Mumbai. He has been visiting professor at Harvard University (2000), the University of California at Berkeley (2001), Oxford University (2002), Sydney University (2009), Soka University (2009), and Savitribai Phule Pune University (2016–17). He has published widely on the Buddhist literature, history, and epigraphy of South and Southeast Asia.
“In this volume, prose and verse join beautifully to celebrate the Dharma. The selections show how rich, how diverse, and how wonderful the Kangyur is—and how little we know about it.” —from the foreword by Dzongsar Jamyang Khyentse
“A stimulating and delightfully readable book . . . Peter Skilling is probably the most versatile scholar of Buddhology today, equally conversant with philosophy, history, ritual, doctrine, art, and iconography. He has selected from the Tibetan twenty-five sutras that were lost in India long ago, which he has translated into elegant English. His introduction and first two appendixes together form a most lucid and up-to-date discussion of Buddhist thought that should be compulsory reading in any field of Buddhology.” —Pratapaditya Pal, author of Quest for Coomaraswamy: A Life in the Arts
“Peter Skilling’s selection of Buddhist sutras comes with an informative introduction, a meticulous exploration of sources, and an attractive and reliable rendering in English. Textual discoveries and expositions of this quality are a substantial contribution to Buddhist studies.” —Romila Thapar, professor emerita of history, Jawaharlal Nehru University, New Delhi
“A magnificent scholar and a magnificent human being, Peter Skilling has always been an example for us all, for his unbounded erudition combined with an unflinching modesty. This precious volume will serve as a reference and an inspiration to present and future generations.”
—Matthieu Ricard, Shechen Monastery, Nepal
QUESTIONING THE BUDDHA
A Selection of Twenty-Five Sutras
In the forty-five years the Buddha spent traversing northern India, he shared his wisdom with everyone from beggar women to kings. Hundreds of his discourses, or sutras, were preserved by his followers, first orally and later in written form. Around thirteen hundred years after the Buddha’s enlightenment, the sutras were translated into the Tibetan language, where they have been preserved ever since. To date, only a fraction of these have been made available in English. Questioning the Buddha brings the reader directly into the literary treasure of the Tibetan canon with thoroughly annotated translations of twenty-five different sutras. Often these texts, many translated here in full for the first time, begin with an encounter in which someone poses a question to the Buddha.
Peter Skilling, an authority on early Buddhist epigraphy, archaeology, and textual traditions, has been immersed in the Buddhist scriptures of diverse traditions for nearly half a century. In this volume, he draws on his deep and extensive research to render these ancient teachings in a fresh and precise language. His introduction is a fascinating history of the Buddhist sutras, including the transition from oral to written form, the rise of Mahayana literature, the transmission to Tibet, the development of canons, and a look at some of the pioneers of sutra study in the West.
Sutras included in this volume are: Four Dharmas Not to Be Taken for Granted; The Benefits of Giving; The Exposition of Four Dharmas; The Merit of the Three Refuges; Four Dharmas Never to Be Abandoned; Advice for Bodhisatva Dharmaketu; Advice for Bodhisatva Jayamati; Sūtra Comparing Bodhicitta to Gold; Bodhisatva Maitreya’s Question about the Gift of the Dharma; Four Summaries of the Dharma Spoken to the Nāga King Sāgara; The Stanza of Dependent Arising; The Heart Formula of Dependent Arising; Prediction of the Boy Brahmaśrī’s Future Buddhahood; Kṣemavatī’s Prediction to Future Buddhahood; The City Beggar Woman; An Old Woman’s Questions about Birth and Death; The Questions of Śrīmatī the Brahman Woman; The Questions of the Laywoman Gaṅgottarā; Brahmā Sahāṃpati’s Question; Advice to King Prasenajit; Passage to the Next Life; Instructions for King Bimbisāra; Instructions for King Udayana; Buddhas as Rare as a Grain of Golden Sand; and Predictions on the Eve of the Great Final Nirvāṇa.
- Learn more about the Classics of Indian Buddhism series.
- 680 pages, 6 x 9 inches
- ISBN 9781614293934
- 680 pages
- ISBN 9781614294085
Coming soon! This book will be published in October 2022. Enter your name and email below to be notified when the book is available for purchase.
This is the epic story of an international rescue effort to preserve a culture’s literary history.
Originally a Mormon from Utah, E. Gene Smith, founder of the Buddhist Digital Resource Center, became the unlikely mastermind behind an international effort to rescue, preserve, digitize, and provide free access to the vast Tibetan Buddhist canon, many volumes of which had been lost or destroyed during China’s Cultural Revolution.
Digital Dharma is a stunning visual experience offering a behind-the-scenes look into this unprecedented mission. Through hundreds of photographs taken during Smith’s trip to deliver drives containing the digitized volumes to remote monasteries in South Asia, you’ll gain extraordinary and intimate access to life inside Buddhist monasteries, to the rituals of Tibetan Buddhism, and to the insights of some of the world’s leading lamas and lineage holders. Throughout the journey, you’ll meet monks, local publishers, scholars, and dignitaries involved in the preservation movement to which Smith dedicated his life. With the accompanying historical and cultural background, you’ll develop a deeper and more personal understanding of Tibetan Buddhism and of the achievement of preserving and disseminating its sacred canon.
The Range of the Bodhisattva, a Mahāyana Sūtra (Ārya-bodhisattva-gocara)
This is a study and the first complete English translation of the Mahāyāna Sūtra, the Bodhi-sattva-gocara, which presents one of the only Buddhist teachings extant on what might be called a “Buddhist theory of war.” The main body of the text takes the form of a dialogue between King Caṇḍapradyota and the Nirgrantha sage, Satyaka, who is later revealed by Śākyamuni Buddha to be a bodhisattva of high attainment.
The author’s introductory essay traces the ways in which the later Indian and Tibetan commentarial traditions have drawn on this sūtra in order to expound upon key themes in Buddhist ethics, law, and state policy, to highlight their positions in opposition to their non-Buddhist contemporaries. From the author’s analysis, it is clear that this sūtra has been seminal in the ethical reflections of generations of Indian and Tibetan Buddhists, though it appears that it was not well known in East Asia.
A companion volume of a Tibetan critical edition is also available.
A History of Buddhism in India and Tibet
The first complete English translation of an important thirteenth-century history that sheds light on Tibet’s imperial past and on the transmission of the Buddhadharma into Central Asia.
Translated here into English for the first time in its entirety by perhaps the foremost living expert on Tibetan histories, this engaging translation, along with its ample annotation, is a must-have for serious readers and scholars of Buddhist studies. In this history, discover the first extensive biography of the Buddha composed in the Tibetan language, along with an account of subsequent Indian Buddhist history, particularly the writing of Buddhist treatises. The story then moves to Tibet, with an emphasis on the rulers of the Tibetan empire, the translators of Buddhist texts, and the lineages that transmitted doctrine and meditative practice. It concludes with an account of the demise of the monastic order followed by a look forward to the advent of the future Buddha Maitreya.
The composer of this remarkably ecumenical Buddhist history compiled some of the most important early sources on the Tibetan imperial period preserved in his time, and his work may be the best record we have of those sources today. Dan Martin has rendered the richness of this history an accessible part of the world’s literary heritage.
Ratnakīrti’s Proof of Momentariness by Positive Correlation (Kṣaṇabhaṇgasiddhi Anvayātmikā)
The Kṣaṇabhaṇgasiddhi is a masterpiece of skillful reasoning by the eleventh-century Indian Buddhist philosopher Ratnakīrti. This renowned scholar taught at the great Buddhist University of Vikramaśīla and was a master of almost every classical philosophical school that preceded him.
The present work is informed by centuries of debate between Buddhist advocates of momentariness and archrival Nyāya philosophers who believed that both selves and things endure.
This book is the first published translation of Ratnakīrti’s proof based on positive correlations, and includes a commentary explaining each step of his reasoning.
Sounds of Innate Freedom, Volume 4
Sounds of Innate Freedom: The Indian Texts of Mahāmudrā are historic volumes containing many of the first English translations of classic mahamudra literature. The texts and songs in these volumes constitute the large compendium called The Indian Texts of the Mahāmudrā of Definitive Meaning, compiled by the Seventh Karmapa, Chötra Gyatso (1456–1539). The collection offers a brilliant window into the richness of the vast ocean of Indian mahamudra texts cherished in all Tibetan lineages, particularly in the Kagyü tradition, giving us a clear view of the sources of one of the world’s great contemplative traditions.
Besides the individual dohās (couplets), vajragītis (vajra songs), and caryāgītis (conduct songs) in this second volume in publication, the three extensive commentaries it contains brilliantly unravel enigmas and bring clarity not only to the specific songs they comment on but to many other, often cryptic, songs of realization in this collection. These expressive songs of the inexpressible offer readers a feast of profound and powerful pith instructions uttered by numerous male and female mahāsiddhas, yogis, and ḍākinīs, often in the context of ritual gaṇacakras and initially kept in their secret treasury. Displaying a vast range of themes, styles, and metaphors, they all point to the single true nature of the mind—mahāmudrā—in inspiring ways and from different angles, using a dazzling array of skillful means to penetrate the sole vital point of buddhahood being found nowhere but within our own mind. Reading and singing these songs of mystical wonder, bliss, and ecstatic freedom, and contemplating their meaning, will open doors to spiritual experience for us today just as it has for countless practitioners in the past.
In Vimalakīrti’s House
Over the course of nearly half a century, Robert A. F. Thurman has left an indelible mark on numerous fields of study, including Buddhist literature, Tantric Buddhism, Tibetan studies, and the comparative sciences of mind. To celebrate his seventieth birthday, Thurman’s students and colleagues have come together to pay tribute to these contributions and to Thurman’s ongoing leadership in these fields by assembling a collection of essays of their own that extend and supplement his groundbreaking research.
In Vimalakīrti’s House is the result of this collaboration and represents a broad spectrum of cutting edge studies in areas central to Thurman’s own scholarly project. The resulting volume is itself a kind of “treasury of the Buddhist sciences,” insofar as its authors explore wide-ranging problems in art, literature, epistemology, history, ritual, buddhology, and lexicography.
Great Treatise on the Stages of Mantra (Sngags rim chen mo)
Tsong Khapa’s Great Treatise on the Stages of Mantra (Sngags rim chen mo)—considered by the present Dalai Lama to be one of Tsong Khapa’s two most important books (along with his Lam rim chen mo)—is his masterful synthesis of the principles and practices of all four classes of Tantra, which formed the basis of his innovation in creating the esoteric “Tantric College” institution and curriculum in the early fifteenth century. With detailed reference to hundreds of works from the Tibetan Kangyur and Tengyur, the chapters presented and studied in this volume concern his treatment of the creation stage (bskyed rim) meditations of Unexcelled Yoga Tantra. This includes a detailed analysis emphasizing how and why such creation stage practices—utilizing deity yoga to transform death, the between, and life into the three bodies of buddhahood are indispensible to creating a foundation for successfully entering the culminal yogic practices of the perfection stage. (A subsequent volume will present the perfection stage chapters of this essential masterwork.)
An important work for both scholars and practitioners, this annotated translation is supplemented with extensive support materials.
The Adamantine Songs (Vajragīti)
Presented here in English for the first time is a set of three of Saraha’s “Adamantine Songs” (Skt. Vajragīti; Tib. rdo rje’i glu), poetic works that play a central role in the Great Seal (mahāmudrā) tantric tradition of both India and Tibet. The tantric adept (siddha) Saraha was among the most notable figures from India’s late first millennium, a time of rich religious and literary activity. His influence on Buddhist practice and poetry extended beyond the Indian subcontinent into Tibet, where it continues to affect every tradition that engages the practice and philosophy of the esoteric Great Seal.
In these songs, Saraha’s views on the nature of mind are presented as both evocative poetry and theoretical exegesis. These songs offer a new perspective on the religious life of Buddhist India and the figure of one of its most famous adepts.
Braitstein opens the door to this important set of texts by Saraha through her elegant translation, critical edition of the Tibetan texts, and in-depth analysis of the three poems. She situates Saraha and his work both in the Tibetan Buddhist sphere and in a broader South Asian literary and religious context, closely treating the central themes in Saraha’s poems, highlighting the specific siddha worldview espoused in his oeuvre, and at the same time unpacking the cryptic references contained in the songs’ individual verses. With this book, Braitstein substantially increases the amount of Saraha’s poetry available to an English-speaking audience and contributes to the ever-increasing movement to explore the culture of the tantric adepts.
Nāgārjuna’s Reason Sixty (Yuktiṣaṣṭikā)
The Reason Sixty is the most concise philosophical work by the second-century Indian Buddhist philosopher Nāgārjuna. It is one of that master’s works most often cited by Centrist (Madhyamaka) commentators, and it is included in the Sixfold Canon of Reason (rigs tshogs drug) which forms the textual basis for Centrist studies in the Tibetan philosophical curriculum. Standing midway between his other masterpieces on philosophy and religion, in the Reason Sixty Nāgārjuna describes the central thrust of his therapeutic philosophy of language—the elimination of cognitive bias and affective resistances to the gradual cultivation of nondualistic wisdom and compassion.
The seventh-century Centrist master Chandrakīrti, concerned with applying his language therapeutic method to define the social epistemology of Centrism, likewise links the critical hermeneutic-pedagogy and the practical therapeutic-anthropology of his other works in his acclaimed Reason Sixty Commentary.
Includes detailed introductory essays, annotated translations, critical Tibetan editions, trilingual glossary, intellectual-historical and biographical tables, bibliography, and index.
“This book is a treasure of subtle revelation.”
—Bonnie Nadzam, Lion’s Roar
The view is the wisdom of being empty
Meditation is luminosity without fixation
Conduct is a continual flow free of attachment
Fruition is nakedness bare of any stain
This is the first stanza of Milarepa’s Ultimate View, Meditation, Conduct, and Fruition: pith instructions originally sang to the great yogi Rechungpa, Milarepa’s disciple. These teachings are Milarepa’s direct offering to his disciple of his own profound realization, gained after many years of dedicated practice. Karl Brunnhölzl, acclaimed translator and senior teacher at the Nalandabodhi community of Dzogchen Ponlop Rinpoche, calls this hard-earned understanding “kungfu”: “Gong means ‘skillful work,’ ‘hard training,’ or ‘endeavor,’ and fu means ‘time spent…’ The term refers to Milarepa’s diligent and skillful training in the techniques to realize the nature of his mind and benefit countless sentient beings.”
Ultimate View, Meditation, Conduct, and Fruition is a work of remarkable depth and clarity. In just five verses, Milarepa gives incisive instructions for progressing and for avoiding pitfalls in the stages of practice:
- View: the basis or ground from which the proper meditation, conduct, and fruition of mahāmudrā can arise
- Meditation: the training in or the familiarization with that view
- Conduct: the natural outflow of having familiarized with the view in meditation
- Fruition: the final outcome of having fully assimilated and realized the view, whose essence is not different from it
Milarepa dedicates one verse to each stage, and Karl dedicates one chapter to each verse, weaving in wisdom from other Milarepa songs, comments by Khenpo Tsultrim Gyatso and from Karl’s own insight. Readers can thus fully immerse themselves in each point of Milarepa’s extraordinary teaching.
“With my diagnosis of grade IV brain cancer, I no longer observe the truth of impermanence from a critical, analytical distance. I am crashing into it, or it into me.”
Facing a terminal cancer diagnosis, Karen Derris—professor, mother, and Buddhist practitioner—instinctually turned to books. By rereading ancient Buddhist stories with fresh questions and a new purpose in mind, she discovered evolving ways to make them immediate and real. Storied Companions interweaves Karen’s memoir of her lived experiences of trauma and terminal illness with stories from Buddhist literary traditions, sharing with the reader how she found ways to live fully even with the reality that she won’t live as long as she needs—or wants.
Using her knowledge, practice, and imagination, Karen illustrates how placing yourself within narratives can turn them from distant and static sources into companions, and from companions into guides. Reading along with her, you’ll realize how this practice of reading and these ancient narratives can help us come to terms with impermanence, develop empathy and compassion, and realize our own interconnectedness.
Honest, powerful, and insightful, Storied Companions itself becomes an invaluable companion, guiding the reader to discover new ways of facing and experiencing life, death, and impermanence.
The Lamp for Integrating the Practices (Caryāmelāpakapradīpa)
The Lamp for Integrating the Practices (Caryāmelāpakapradīpa) by Āryadeva, is a systematic and comprehensive exposition of the most advanced yogas of the Esoteric Community Tantra (Guhyasamāja-tantra) as espoused by the Noble (Nāgārjuna) tradition, an influential school of interpretation within Indian Buddhist mysticism. Equal in authority to Nāgārjuna’s famous Five Stages (Pañcakrama), Āryadeva’s work is perhaps the earliest prose example of the “stages of the mantra path” genre in Sanskrit. Its systematic path exerted immense influence on later Indian and Tibetan traditions, and it is widely cited by masters from all four major lineages of Tibetan Buddhism.
This volume presents the Lamp in a thoroughly annotated English translation. It includes an introductory study discussing the history of the Guhyasamāja and its exegetical traditions, surveying the scriptural and commentarial sources of the Nāgārjuna tradition, and analyzing in detail the contents of the Lamp. The book also features a detailed, trilingual glossary.
Simultaneously presented online for scholars are a version of its Sanskrit original, critically edited from recently identified manuscripts, and a critical edition of the eleventh-century Tibetan translation by Rinchen Zangpo, including notes on readings found in “lost,” alternative translations.
Four Tibetan Lineages
The newest translation from master translator Sarah Harding.
Drawing primarily from the Pacification, Severance, Shangpa Kagyü, and Bodongpa traditions, Four Tibetan Lineages presents some of Tibet’s most transformative yet lesser-known teachings on meditative practice. Most works in this volume are drawn from a Tibetan anthology known as the Treasury of Precious Instructions compiled by Jamgön Kongtrul Lodrö Thayé (1813–1900). A vast preservation project, this anthology reflects Kongtrul’s attempt to rescue rare teachings from disappearing. By foregrounding the teachings of masters like Khedrup Khyungpo Naljor (d. 1135), Dampa Sangyé (d. 1117), Machik Labdrön (1031/55–1126/50), Jonang Tāranātha (1575–1634), and Jamyang Khyentsé Wangpo (1820–92), this volume extends Jamgön Kongtrul’s preservation efforts into the modern world.
The Play of Mahamudra
“This new collected edition of Khenpo Migmar Tseten’s Play of Mahamudra volumes constitutes a veritable treasure for all who are deeply engaged on the path to enlightenment. Khenpo Migmar’s translation of Mahasiddha Virupa’s Treasury of Dohas and of Sachen Kunga Nyingpo’s Praise to Virupa makes us intimately familiar with the essence of these root texts, and his elucidation of the Dohas offers us a deep and clear understanding of their core meaning. Anyone who truly contemplates on Mahasiddha Virupa’s words is certain to attain realization.”
—His Holiness the Sakya Trichen
In this collection, renowned Tibetan Buddhist teacher Lama Migmar Tseten provides essential commentary on the mystical songs of the Indian Buddhist rebel-saint Virupa. One of the most celebrated tantric masters of Buddhist India, Virupa’s songs describe his realization of mahamudra, the ultimate nature of reality. Intimate and highly engaging, The Play of Mahamudra unpacks these songs with meticulous clarity, making Virupa’s insights accessible to modern readers.
“Gharwang Rinpoche’s work serves as a definitive manual, guiding aspiring mahāmudrā students along the complete path, beginning with a clear presentation of the preliminaries, through a detailed presentation of śamatha and vipaśyanā, and concluding with enlightening instructions on the actualization of the result.”
—from the foreword by His Holiness the Sakya Trichen
In this book, His Eminence the Twelfth Zurmang Gharwang Rinpoche offers illuminating commentary on Bokar Rinpoche’s pithy teaching A Concise Commentary on the Ocean of Definitive Meaning, expanding and unlocking it for the reader, showing us the way to understand the very nature of our own minds.
“The line between saṃsāra and nirvāṇa is very thin. This is because saṃsāra is simply the projection of our minds, a projection created by confusion. Nirvāṇa is simply freedom from this confusion. You can sit on either side of the line between saṃsāra and nirvāṇa. It’s up to you. But although the line is very thin, it takes extraordinary skill and profound wisdom to traverse the path from one side to the other—to dissolve the division itself. This book and these teachings are intended to serve as support for that journey.”
—from H.E. Zurmang Gharwang Rinpoche’s introduction
Superiority Conceit in Buddhist Traditions
Armed with his rigorous examination of the canonical records, respected scholar-monk Bhikkhu Anālayo explores—and sharply criticizes—four examples of what he terms “superiority conceit” in Buddhism:
- the androcentric tendency to prevent women from occupying leadership roles, be these as fully ordained monastics or as advanced bodhisattvas
- the Mahayana notion that those who don’t aspire to become bodhisattvas are inferior practitioners
- the Theravada belief that theirs is the most original expression of the Buddha’s teaching
- the Secular Buddhist claim to understand the teachings of the Buddha more accurately than traditionally practicing Buddhists
Ven. Anālayo challenges the scriptural basis for these conceits and points out that adhering to such notions of superiority is not, after all, conducive to practice. “It is by diminishing ego, letting go of arrogance, and abandoning conceit that one becomes a better Buddhist,” he reminds us, “no matter what tradition one may follow.”
Thoroughly researched, Superiority Conceit in Buddhist Traditions provides an accessible approach to these conceits as academic subjects. Readers will find it not only challenges their own intellectual understandings but also improves their personal practice.
Sounds of Innate Freedom, Volume 5
Sounds of Innate Freedom: The Indian Texts of Mahāmudrā are historic volumes containing many of the first English translations of classic mahāmudrā literature. The texts and songs in these volumes constitute the large compendium called The Indian Texts of the Mahāmudrā of Definitive Meaning, compiled by the Seventh Karmapa, Chötra Gyatso (1456–1539). The collection offers a brilliant window into the richness of the vast ocean of Indian Mahāmudrā texts cherished in all Tibetan lineages, particularly in the Kagyü tradition, giving us a clear view of the sources of one of the world’s great contemplative traditions.
This first volume in publication contains the majority of songs of realization, consisting of dohās (couplets), vajragītis (vajra songs), and caryāgītis (conduct songs), all lucidly expressing the inexpressible. These songs offer readers a feast of profound and powerful pith instructions uttered by numerous male and female mahasiddhas, yogīs, and ḍākinīs, often in the context of ritual gaṇacakras and initially kept in their secret treasury. Displaying a vast range of themes, styles, and metaphors, they all point to the single true nature of the mind—mahāmudrā—in inspiring ways and from different angles, using a dazzling array of skillful means to penetrate the sole vital point of buddhahood being found nowhere but within our own mind. Reading and singing these songs of mystical wonder, bliss, and ecstatic freedom, and contemplating their meaning in meditation, will open doors to spiritual experience for us today just as it has for countless practitioners in the past.
Science and Philosophy in the Indian Buddhist Classics, Vol. 2
This, the second volume in the Science and Philosophy in the Indian Buddhist Classics series, focuses on the science of mind. Readers are first introduced to Buddhist conceptions of mind and consciousness and then led through traditional presentations of mental phenomena to reveal a Buddhist vision of the inner world with fascinating implications for the contemporary disciplines of cognitive science, psychology, emotion research, and philosophy of mind. Major topics include:
- The distinction between sensory and conceptual processes and the pan-Indian notion of mental consciousness
- Mental factors—specific mental states such as attention, mindfulness, and compassion—and how they relate to one another
- The unique tantric theory of subtle levels of consciousness, their connection to the subtle energies, or “winds,” that flow through channels in the human body, and what happens to each when the body and mind dissolve at the time of death
- The seven types of mental states and how they impact the process of perception
- Styles of reasoning, which Buddhists understand as a valid avenue for acquiring sound knowledge
In the final section, the volume offers what might be called Buddhist contemplative science, a presentation of the classical Buddhist understanding of the psychology behind meditation and other forms of mental training.
To present these specific ideas and their rationale, the volume weaves together passages from the works of great Buddhist thinkers like Asaṅga, Vasubandhu, Nāgārjuna, Dignāga, and Dharmakīrti. His Holiness the Dalai Lama’s introduction outlines scientific and philosophical thinking in the history of the Buddhist tradition. To provide additional context for Western readers, each of the six major topics is introduced with an essay by John D. Dunne, distinguished professor of Buddhist philosophy and contemplative practice at the University of Wisconsin. These essays connect the traditional material to contemporary debates and Western parallels, and provide helpful suggestions for further reading.