Conceptualising Duolingo and its Affordances and Constraints as a Learning Tool in ESL Reading Classrooms: A Concept Paper

Abdullah, M. Y., Hussin, S., & Ismail, K. (2019). Implementation of flipped classroom model and its effectiveness on English speaking performance. International Journal of Emerging Technologies in Learning (Online), 14(9), 130-147.
https://doi.org/10.3991/ijet.v14i09.10348
Afzal, N. (2019). A study on vocabulary-learning problems encountered by BA English majors at the university level of education. Arab World English Journal (AWEJ), 10(3),81-98. https://dx.doi.org/10.2139/ssrn.3465990
Ahmed, A. A. A., Hassan, I., Pallathadka, H., Keezhatta, M. S., Noorman Haryadi, R., Al Mashhadani, Z. I., & Rohi, A. (2022). MALL and EFL learners’ speaking: Impacts of Duolingo and WhatsApp applications on speaking accuracy and fluency. Education Research International, 1-10. https://doi.org/10.1155/2022/6716474
Ajisoko, P. (2022). Using Duolingo apps to improve English reading comprehension of engineering students in Universitas Borneo Tarakan. Exposure: Jurnal Pendidikan Bahasa Inggris,11(1), 1-6. https://journal.unismuh.ac.id/index.php/exposure
Al-Jarf, R. (2022). Specialized dictionary mobile apps for students learning English for engineering, business, and computer science. Journal of Humanities and Education Development (JHED), 4(1), 1-9. https://dx.doi.org/10.22161/jhed.4.1.1
Al Raqqad, Y. M., Ismail, H. H., & Al Raqqad, K. M. (2019). The impact of reading strategies on EFL students: A research review. International Journal of English Literature and Social Sciences (IJELS), 4(6), 2042-2048 http://dx.doi.org/10.22161/ijels.46.65
Alobaid, A. (2020). Smart multimedia learning of ICT: Role and impact on language learners’ writing fluency—YouTube online English learning resources as an example. Smart Learning Environments, 7(1), 7-24.
https://slejournal.springeropen.com/articles/10.1186/s40561-020-00134-7
Alyousef, H. S. (2006). Teaching Reading Comprehension to ESL / EFL Learners. Journal of Language and Learning, 5(1), 379–380.
Amin, M. (2019). The role of educational technology in the ESL classroom. Global Journal of Archaeology & Anthropology, 11(1), 191-
213. https://dx.doi.org/10.2139/ssrn.3488369
Amin, S. N. (2021). Gamification of Duolingo in rising students’ English language learning motivation. Jurnal Bahasa Lingua Scientia, 13(2), 191-
213. https://doi.org/10.21274/ls.2021.13.2.191-213
Anak Yunus, C. C., & Hua, T. K. (2021). Exploring a gamified learning tool in the ESL classroom: The case of Quizizz. Journal of Education and e-Learning Research, 8(1), 103-108. http://dx.doi.org/10.20448/journal.509.2021.81.103.108
Ariffin, A. (2021). Effects of student collaboration on ESL learners' vocabulary development. Asian Journal of University Education, 17(1), 177-
191. https://doi.org/10.24191/ajue.v17i1.12627
Avelino, N. M., & Ismail, H. H. (2021). Assessing ESL teachers’ knowledge and readiness in integrating 4IR into teaching practices: A concept paper. Creative Education, 12(9), 2038- 2055. http://dx.doi.org/10.4236/ce.2021.129156
Aziz, A. A., & Kashinathan, S. (2021). ESL learners’ challenges in speaking English in Malaysian classroom. Development, 10(2),983-991. http://dx.doi.org/10.6007/IJARPED/v10-i2/10355
Azmi, N. (2017). The benefits of using ICT in the EFL classroom: from perceived utility to potential challenges. Journal of Educational and Social Research, 7(1), 111-118. http://dx.doi.org/10.5901/jesr.2017.v7n1p111
Blututors. (2016). Artificial intelligence – Will smart computers replace teachers? BlueTutors. https://bluetutors.co.uk/tuition-articles/2016/dec/bluetutors-articles/artificial intelligencewill-smart-computers-replace-teachers.
Bouranta, N., Chitiris, L., & Paravantis, J. (2009). The relationship between internal and external service quality. International Journal of Contemporary Hospitality Management, 21(3), 275-293. http://dx.doi.org/10.1108/09596110910948297
Brown, H. D. (2004). Language Assessment: Principles and Classroom Practices. London, UK: Longman Group UK Ltd.
Burstein, J., LaFlair, G. T., Kunnan, A. J., & von Davier, A. A. (2021). A theoretical assessment ecosystem for a digital-first assessment—The Duolingo English Test. DRR-21-04.
Cakici, D. (2015). Autonomy in language teaching and learning process. ?nönü Üniversitesi E?itim Fakültesi Dergisi ,16(1), 31-42. http://dx.doi.org/10.17679/iuefd.16168538
Desnita, D., Putra, A., Hamida, S., Marsa, P. B., & Novisya, D. (2021). Quality Test of Student Worksheets Based on Contextual Teaching And Learning for Class XI High School Physics. Jurnal Penelitian Pendidikan IPA. 7(1), 92-101. https://doi.org/10.29303/jppipa.v7i1.600
Edwards, B. I., & Cheok, A. D. (2018). Why not robot teachers: artificial intelligence for addressing teacher shortage. Applied Artificial Intelligence, 32(4), 345-360. https://doi.org/10.1080/08839514.2018.1464286
Erfiani, E., & Miski, C. R. (2022). The use of Duolingo in enhancing students' vocabulary mastery at SMA Negeri 3 Bangko Pusako during pandemic Covid-19. Indonesian Journal of Integrated English Language Teaching, 8(1), 55-62.
http://dx.doi.org/10.24014/ijielt.v8i1.17972
Evans, E. (2017). Learning from high school students' lived experiences of reading e-books and printed books. Journal of Adolescent and Adult Literacy, 61(3),311-318. https://doi.org/10.1002/jaal.685
Fansury, A. H., Januarty, R., & Ali Wira Rahman, S. (2020). Digital content for millennial generations: Teaching the English foreign language learner on COVID-19 pandemic. Journal of Southwest Jiaotong University, 55(3), 1-12. https://doi.org/10.35741/issn.0258-2724.55.3.40
Garcia, I. (2013). Learning a language for free while translating the web. Does Duolingo work? International Journal of English Linguistics, 3(1), 288-301. http://dx.doi.org/10.5539/ijel.v3n1p19
Habibie, A. (2020). Duolingo as an educational language tool to enhance EFL students’ motivation in writing. British (Jurnal Bahasa dan Sastra Inggris), 9(1), 13-26.
Hakimantieq, H., Suherdi, D., & Gunawan, W. (2022). Duolingo as a mobile-assisted language learning: A new supplementary of learning basic English reading for EFL students. EDUKATIF: JURNAL ILMU PENDIDIKAN, 4(6), 7548-7558.
Haleem, A., Javaid, M., Qadri, M. A., & Suman, R. (2022). Understanding the role of digital technologies in education: A review. Sustainable Operations and Computers, 3, 275-285. https://doi.org/10.1016/j.susoc.2022.05.004
Hashim, H., Yunus, M. M., & Embi, M. A. (2018). Learning through mobile: Exploring the views of polytechnic ESL learners. Teaching and Learning English in Multicultural Contexts (TLEMC), 2, 56-62. https://doi.org/10.37058/tlemc.v2i1.490
Hashim, H., Rafiq, R. M., & Md Yunus, M. (2019). Improving ESL learners’ grammar with gamified learning. Arab World English Journal (AWEJ) Special Issue on CALL, (5), 41-50. http://dx.doi.org/10.31235/osf.io/xar32
Hashim, H., Yunus, M. M., Embi, M. A., & Ozir, N. A. M. (2017). Mobile-assisted language learning (MALL) for ESL learners: A review of affordances and constraints. Sains Humanika, 9(1-5),45-50. https://doi.org/10.11113/sh.v9n1-5.1175
Hedgcock, J. S., & Ferris, D. R. (2018). Teaching readers of English: Students, texts, and contexts. Routledge.
Hidayati, T., & Diana, S. (2019). Students’ motivation to learn English using mobile applications: The case of Duolingo and Hello English. JEELS Journal of English Education and Linguistics Studies, 6(2), 189-213. http://dx.doi.org/10.30762/jeels.v6i2.1233
Huynh, D., Zuo, L., & Iida, H. (2018). An assessment of game elements in language-learning platform Duolingo. In 2018 4th International Conference on Computer and Information Sciences (ICCOINS), 1–4. http://dx.doi.org/10.1109/ICCOINS.2018.8510568
Huy, V. Q. (2023). The benefits of Duolingo software in learning Japanese and what makes it different from other applications. Journal of Optoelectronics Laser, 42(4), 5-8.
Jaikrishnan, S., & Ismail, H.H. (2021). A review on vocabulary learning strategies used in learning English as a second language. Sciences, 11(9), 297-309. http://dx.doi.org/10.6007/IJARBSS/v11-i9/10512
Jamieson, S. (2004). Likert scales: How to (ab) use them? Medical education, 38(12), 1217-1218. http://dx.doi.org/10.1111/j.1365-2929.2004.02012.x
Jiang, X., Rollinson, J., Plonsky, L., Gustafson, E., & Pajak, B. (2021). Evaluating the reading and listening outcomes of beginning?level Duolingo courses. Foreign Language Annals, 54(4), 974-1002. https://doi.org/10.1111/flan.12600
Joo, S. J., Chik, A., & Djonov, E. (2020). The construal of English as a global language in Korean EFL textbooks for primary school children. Asian Englishes, 22(1), 68-84. http://dx.doi.org/10.1080/13488678.2019.1627636
Jung, S. K. (2019). Introduction to popular mobile chatbot platforms for English learning: Trends and issues. STEM Journal, 20(2), 67-90.
https://doi.org/10.16875/stem.2019.20.2.67
Kacetl, J., & Klímová, B. (2019). Use of smartphone applications in English language learning – A challenge for foreign language education. Education Sciences 9(3): 179- 187 https://doi.org/10.3390/educsci9030179
Kang, J. (2021). Digital technical language teaching----Teaching/Learning principles of Duolingo. Learning & Education, 10(2), 50-51.
Kao, G. Y. M., Chiang, X. Z., & Foulsham, T. (2019). Reading behavior and the effect of embedded selfies in role-playing picture e-books: An eye-tracking investigation. Computers & Education, 136, 99-112.
http://dx.doi.org/10.1016/j.compedu.2019.03.010
Kaynar, N., Sadik, O., & Boichuk, E. (2020). Technology in early childhood education: Electronic books for improving students’ literacy skills. TechTrends, 64, 911-921. http://dx.doi.org/10.1007/s11528-020-00520-5
Kessler, M. (2023). Supplementing mobile-assisted language learning with reflective journal writing: A case study of Duolingo users’ metacognitive awareness. Computer Assisted Language Learning, 36(5-6), 1040-
1063. http://dx.doi.org/10.1080/09588221.2021.1968914
Krashen, S., Mason, B., & Smith, K. (2014). Can we increase the power of reading by adding communicative output activities? A comment on song and sardegna (2014). RELC Journal, 45(2), 211-212. https://doi.org/10.1177/0033688214539866
Li, J., Xie, P., Ai, B., & Li, L. (2020). Multilingual communication experiences of international students during the COVID-19 pandemic. Multilingua, 39(5), 529-539. http://dx.doi.org/10.1515/multi-2020-0116
Liang, L. (2018). Exploring language learning with mobile technology: A qualitative content analysis of vocabulary learning apps for ESL learners in Canada. Master Thesis, the University of Ontario.
Lim, T. M., & Yunus, M. M. (2021). Teachers’ perception towards the use of Quizizz in the teaching and learning of English: A systematic review. Sustainability, 13(11), 6436. https://doi.org/10.3390/su13116436
Loh, C. E., & Sun, B. (2019). “I'd still prefer to read the hard copy”: Adolescents’ print and digital reading habits. Journal of Adolescent & Adult Literacy, 62(6), 663-672. http://dx.doi.org/10.1002/jaal.904
Lumapenet, H. (2022). Multimedia: A Tool in Addressing the Reading Difficulties of Learners. International Journal of Early Childhood Special Education, 14(1), 2357-2362. http://dx.doi.org/10.9756/INT-JECSE/V14I1.276
Mahanal, S., Zubaidah, S., Sumiati, I. D., Sari, T. M., & Ismirawati, N. (2019). RICOSRE: A Learning Model to Develop Critical Thinking Skills for Students with Different Academic Abilities. International Journal of Instruction, 12(2), 417-434. https://doi.org/10.29333/iji.2019.12227a
Mahdi, Q. S., Saleh, I. H., Hashim, G., & Loganathan, G. B. (2021). Evaluation of robot professor technology in teaching and business. Information Technology in Industry, 9(1), 1182-1194. http://dx.doi.org/10.17762/itii.v9i1.255
Mandasari, B., & Aminatun, D. (2020). Improving students’ speaking performance through Vlog. English Education: Journal of English Teaching and Research, 5(2), 136-142. https://doi.org/10.29407/jetar.v5i2.14772
Mangen, A., Olivier, G., & Velay, J. L. (2019). Comparing comprehension of a long text read in print book and on Kindle: Where in the text and when in the story? Frontiers in psychology, 10, 38. https://doi.org/10.3389/fpsyg.2019.00038
Md Yunus, M., Hashim, H. U., Makhtar, R., Norman, H., & Hashim, H. (2020). The voyage of ESL learners’ English language learning in the era of postcolonialism: A thematic analysis. Humanities and Social Sciences Letters, 8(2), 224-229. http://dx.doi.org/10.18488/journal.73.2020.82.224.229
Milyarni, F. D., Mortini, A. V., & Mayasari, S. (2021). Translation exercises of English to Indonesian in Duolingo application. The Journal of English Literacy Education: The Teaching and Learning of English as a Foreign Language, 8(2), 150-163. http://dx.doi.org/10.36706/jele.v8i2.15531
Mishra, S.B.; Alok, S. (2022). Handbook of Research Methodology. Educreation Publishing, Chhattisgarh, India.
Mohaideen, M. S. H., Ismail, H. H., & Ab Rashid, R. (2020). The use of local literary texts as reading materials in English language classrooms: An analysis of teachers' perspectives. International Journal of Learning, Teaching and Educational Research, 19(11), 127-144. http://dx.doi.org/10.26803/ijlter.19.11.8
Mohajan, H. K. (2020). Quantitative research: A successful investigation in natural and social sciences. Journal of Economic Development, Environment and People 9(4): 50-79.
Munday, P. (2016). The case for using Duolingo as part of the language classroom experience. RIED: revista iberoamericana de educación a distancia, 19(1), 83-101. http://dx.doi.org/10.5944/ried.19.1.14581
Nasichah, A. H., Ningsih, A. P., Sabrina, M., & Hasanah, N. (2022). Analyzing students’ perception about the use of Duolingo application towards vocabulary mastery at UIN Prof KH Saifuddin Zuhri Purwokerto. In Conference on English Language Teaching pp. 65-78. http://dx.doi.org/10.24090/celti.v2.37
Nasir, N. A. M., & Aziz, A. A. (2020). Implementing student-centered collaborative learning when teaching productive skills in an ESL primary classroom. International Journal of Publication and Social Studies, 5(1), 44-54.
http://dx.doi.org/10.18488/journal.135.2020.51.44.54
Noordan, M. N. H., & Yunus, M. M. (2022). The Integration of ICT in Improving Reading Comprehension Skills: A Systematic Literature Review. Creative Education, 13(6), 2051-2069. http://dx.doi.org/10.4236/ce.2022.136127
Nufus, Z., & Ifadloh, N. (2021). The Realization of Brown’s Theory of Assessing Reading on Reading Section of English National Examination. SALEE: Study of Applied Linguistics and English Education, 2(2), 182-191. https://dx.doi.org/10.35961/salee.v2i02.288
Nur, L., Ginanjar, A., Malik, A. A., & Pingon, L. (2021). Validity and reliability of elementary school students' learning motivation instruments in physical education. Jurnal Maenpo: Jurnal Pendidikan Jasmani Kesehatan Dan Rekreasi, 11(2), 205-215. http://dx.doi.org/10.35194/jm.v11i2.1843
Parker, C., Scott, S., & Geddes, A. (2019). Snowball sampling. SAGE research methods foundations. California: SAGE Publication.
Pazilah, F. N. P., Hashim, H., & Yunus, M. M. (2019). Using technology in ESL classroom: Highlights and challenges. Creative Education, 10(12), 3205- 3212 https://doi.org/10.4236/ce.2019.1012244
Pratasik, G. (2022). Learning English vocabulary through the Duolingo application to help young learners’ reading skill. Journal of English Language Teaching, Literature and Culture, 1(1), 54-60. https://doi.org/10.2503/jeltec.v1i1.3726
Putri, L. M., & Islamiati, A. 2018. Teaching listening using Duolingo application. Journal of English Education 1(4): 460-465
Rafiq, K. R. M., Hashim, H., & Yunus, M. M. (2021). Sustaining education with mobile learning for English for specific purposes (Esp): A systematic review (2012–2021). Sustainability, 13(17), 9768. http://dx.doi.org/10.3390/su13179768
Rajasagaran, S., & Ismail, H. H. (2022). Utilising Explicit Teaching of Metacognitive Strategies in Honing Reading Skills among ESL and EFL Learners: A Review. International Journal of Academic Research in Progressive Education & Development, 11(3), 1138–1158. http://dx.doi.org/10.6007/IJARPED/v11-i3/14997
Rajendran, T., & Yunus, M. M. (2021). A systematic literature review on the use of mobile assisted language Learning (MALL) for enhancing speaking skills among ESL and EFL learners. International Journal of Academic Research in Progressive Education and Development, 10(1), 586-609. http://dx.doi.org/10.6007/IJARPED/v10-i1/8939
Raw, S. D. M., & Ismail, H. H. (2021). Tracing effectiveness and challenges in using online tools to enhance vocabulary language learning: A Review. International Journal of Academic Research in Progressive Education and Development. 10(3), 938-952. http://dx.doi.org/10.6007/IJARPED/v10-i3/10756
Redjeki, I. S., & Muhajir, R. (2021). Gamification in EFL classroom to support teaching and learning in 21st century. JEES (Journal of English Educators Society), 6(1), 68-78. http://dx.doi.org/10.21070/jees.v6i1.882
Rintaningrum, R. (2019). Explaining the important contribution of reading literacy to the country’s generations: Indonesian’s perspectives. Journal of Turkish Science Education, 11(1), 3-23.
Ritonga, M., Febriani, S. R., Kustati, M., Khaef, E., Ritonga, A. W., & Yasmar, R. (2022). Duolingo: An Arabic speaking skills’ learning platform for andragogy education. Education Research International, 2022, 1-9 http://dx.doi.org/10.1155/2022/7090752
Rohaizat, N., & Aziz, A. A. (2021). Systematic Literature Review of Language Learning Strategies for Reading Skills in English for Specific Purposes among Business Students. International Journal of Academic Research in Business and Social Sciences, 11(12), 139-159 http://dx.doi.org/10.6007/IJARBSS/v11-i12/11522
Salleh, P. N. A. B. M., & Ismail, H. H. (2022). Paddling through the Learning of Literature Using ICT: A Review on Students’ Perception 11(3):1860–
1871 https://dx.doi.org/10.6007/IJARPED/v11-i3/15050
Sani, S., & Ismail, H. H. (2021). Assessing the use of learning strategies among young Malaysian English as second language learners. Creative Education, 12, 2124-2145. https://doi.org/10.4236/ce.2021.129163
Saraswati, N. A., & Purwati, O. (2021). Autonomous mobile-assisted language learning for young learners using Duolingo. Celtic: A Journal of Culture, English Language Teaching, Literature and Linguistics, 8(2), 235-246. https://doi.org/10.22219/celtic.v8i2.16959
Shortt, M., Tilak, S., Kuznetcova, I., Martens, B., & Akinkuolie, B. (2021). Gamification in mobile-assisted language learning: A systematic review of Duolingo literature from public release of 2012 to early 2020. Computer Assisted Language Learning, 1-38. http://dx.doi.org/10.1080/09588221.2021.1933540
Shortt, M., Tilak, S., Kuznetcova, I., Martens, B., & Akinkuolie, B. (2023). Gamification in mobile-assisted language learning: A systematic review of Duolingo literature from public release of 2012 to early 2020. Computer Assisted Language Learning, 36(3), 517-554. https://doi.org/10.1080/09588221.2021.1933540
Singer, L. M., & Alexander, P. A. (2017). Reading across mediums: Effects of reading digital and print texts on comprehension and calibration. The journal of experimental education, 85(1), 155-172. http://dx.doi.org/10.1080/00220973.2016.1143794
Sivagnanam, S., & Yunus, M. M. (2020). Utilizing social media in vocabulary enhancement among primary ESL learners. Universal Journal of Educational Research, 8(2), 490-498. http://dx.doi.org/10.13189/ujer.2020.080220
Snow, C. (2002). Reading for understanding: Toward an R&D program in reading comprehension. Rand Corporation.
Sun, Y., & Gao, F. (2020). An investigation of the influence of intrinsic motivation on students’ intention to use mobile devices in language learning. Educational Technology Research & Development. https://doi.org/10.1007/s11423-019-09733-9
Syahputra, M. (2019). Duolingo gamification: Does it reduce students’ grammatical errors in writing? Getsempena English Education Journal, 6(1), 1-12. https://doi.org/10.46244/geej.v6i1.858
Tiara, A. D., Rahman, M. A., & Handrianto, C. (2021). The student’s perception about use of Duolingo application for improving English vocabulary. International Journal of Education, Information Technology, and Others, 4(4), 690-701. http://dx.doi.org/10.5281/zenodo.5775915
Toro, V., Camacho-Minuche, G., Pinza-Tapia, E., & Paredes, F. (2019). The Use of the Communicative Language Teaching Approach to Improve Students' Oral Skills. English Language Teaching, 12(1), 110-118. https://doi.org/10.5539/elt.v12n1p110
Tsai, N. (2022). Learning Polish with Duolingo: A case study in Taiwanese academic setting. Acta Universitatis Lodziensis. Kszta?cenie Polonistyczne Cudzoziemców, (29), 31-52. http://dx.doi.org/10.18778/0860-6587.29.03
Uttley, J. (2019). Power analysis, sample size, and assessment of statistical assumptions— Improving the evidential value of lighting research. Leukos, 15(2-3), 143-162. https://doi.org/10.1080/15502724.2018.1533851
Vasileiou, I., & Pili-Moss, D. (2022). The role of learners’ memory in app-based language instruction: the case of Duolingo. Intelligent CALL, granular systems and learner data: short papers from EUROCALL 2022
364. http://dx.doi.org/10.14705/rpnet.2022.61.1485
Yana, D. (2021). Applying Duolingo as English learning media: How do students perceive it? International Journal of Language Pedagogy, 1(2), 62-
66. https://doi.org/10.24036/ijolp.v1i2.11
Yunus, M. M., & Azman, M. A. (2019). Memory stay or stray? irregular verbs learning using Kahoot! Arab World English Journal (AWEJ) Special Issue on CALL 5, 206-219. http://dx.doi.org/10.24093/awej/call5.15
Yusra, A., Neviyarni, S., & Erianjoni, E. (2022). A Review of behaviorist learning theory and its impact on the learning process insSchools. International Journal of Educational Dynamics, 5(1), 81-91. https://doi.org/10.24036/ijeds.v5i1.373
Yunus, M. M., Yaacob, N., & Suliman, A. (2020). The Use of Electronic Frog VLE in Assisting Reading Comprehension Activities. Universal Journal of Educational Research, 8(3), 879-887. http://dx.doi.org/10.13189/ujer.2020.080319
Zakaria, S., Salam, A. R. H., & Kew, S. N. (2022). Gamification and collaborative learning among English second language culinary learners. International Journal of Education and Pedagogy, 4(1), 8-
18. https://myjms.mohe.gov.my/index.php/ijeap/article/view/16959
Zakaria, N. Y. K., Azmi, N. E., & Hadi, N. A. A. (2019). Improving Reading Skills Using Language Learning Strategies (LLS). Journal of Counseling and Educational Technology, 2(1), 1-5. http://dx.doi.org/10.32698/0271
Zhao, J., Hwang, G. J., Chang, S. C., Yang, Q. F., & Nokkaew, A. (2021). Effects of gamified interactive e-books on students’ flipped learning performance, motivation, and meta-cognition tendency in a mathematics course. Educational Technology Research and Development, 69, 3255-3280. http://dx.doi.org/10.1007/s11423-021-10053-0

N/A

Copyright: © 2023 The Author(s)
Published by HRMARS (www.hrmars.com)
This article is published under the Creative Commons Attribution (CC BY 4.0) license. Anyone may reproduce, distribute, translate and create derivative works of this article (for both commercial and non-commercial purposes), subject to full attribution to the original publication and authors. The full terms of this license may be seen at: http://creativecommons.org/licences/by/4.0/legalcode