1 I. Kant, ‘An Old Question Raised Again: Is the Human Race Constantly Progressing?’ OQ 85, cited by C. Korsgaard, ‘Taking the Law into Our Own Hands: Kant on the Right to Revolution’, in Reath, A., Herman, B., and Korsgaard, C. M. (eds.), Reclaiming the History of Ethics: Essays for John Rawls (1997), 297 at 299CrossRefGoogle Scholar.

2 See Panara, C. and Wilson, G. (eds.), The Arab Spring: New Patterns for Democracy and International Law (2013)CrossRefGoogle Scholar; R. Albert, ‘Democratic Revolutions’, unpublished manuscript, on file with author (12 April 2011); Varol, O. O., ‘The Democratic Coup D’Etat’, (2012) 53 Harv. Int’l L. J.Google Scholar; Paust, J. J., ‘International Law, Dignity, Democracy, and the Arab Spring’, (2013) 46 Cornell Int’l L. J.Google Scholar; J. M. Powell, ‘An Assessment of the Democratic Coup Theory: Democratic Trajectories in Africa’, 1952–2012, May 2014, available at <papers.ssrn.com/sol3/papers.cfm?abstract_id=2443766>.

3 Sub-Saharan countries that experienced varying degrees of popular protests following the North-African uprisings include Burkina Faso, Senegal, Cameroon, Benin, Swaziland, Botswana, Mozambique, Malawi, Uganda, Sudan, Djibouti, and Ethiopia.

4 AU PSC, Communiqué, PSCPR/COMM. (CCLX), 16 February 2011.

5 AU PSC, Communiqué, PSCPR/COMM. (CCLXI), 23 February 2011.

6 AU PSC, Communiqué, PSCPR/COMM. (CCLXV), 10 March 2011.

7 See Security Council, Press Release, SC/10200, ‘Security Council Approves “No-Fly Zone” over Libya, Authorizing “All Necessary Measures” to Protect Civilians, by Vote of 10 in Favor with 5 Abstentions’, 17 March 2011, available at <www.un.org/News/Press/docs/2011/sc10200.doc.htm#Resolution>.

8 Ibid.

9 AU PSC, Communiqué, PSC/PR/2 (CCLXXV), 26 April 2011.

10 S. A. Dersso, ‘Reflections on the Adequacy and Potential of the APSA for Responding to Popular Uprisings’, in Souaré, I. K. and Mesfin, B. (eds.), A Critical Look at the 2011 North African Revolutions and their Implications (31 May 2011) ISS Conference ReportGoogle Scholar. See also K. Sturman, ‘Unconstitutional Changes of Government: The Democrat's Dilemma in Africa’ (March 2011) 30 SAIIA Policy Briefing, available at <www.saiia.org.za/images/stories/pubs/briefings/saia_spb_30_sturman_20110322.pdf>.

11 AU PSC, Communiqué, PSCPR/COMM. (CCCLXXXIV), 5 July 2013.

12 In his televised statement that declared the end of Morsi's presidency, general Abdel Fattah al-Sisi stated that the army ‘has been called by the Egyptian people for help’ and needed to ‘discharge its civil responsibility’. An English version of the transcript of the Egyptian army's statement is available at <www.aljazeera.com/news/middleeast/2013/07/201373203740167797.html>;. See also O. Housden, ‘Egypt: Coup d’Etat or a Revolution Protected?’, (2013) 158 The RUSI Journal 72.

13 H. Kelsen, General Theory of Law and State (1949), 368.

14 See Paust, supra note 2.

15 A. de Tocqueville, Democracy in America, Vols. I and II, trans. H. Reeves (2002), available at <www2.hn.psu.edu/faculty/jmanis/toqueville/dem-in-america1.pdf>.

16 Ibid., at 577.

17 R. R. Palmer, The Age of the Democratic Revolution (1959); see also A. Potofsky, ‘The One and the Many: The Two Revolutions Question and the “Consumer-Commercial” Atlantic, 1789 to the Present’, in Albertone, M. and De Francesco, A. (eds.), Rethinking the Atlantic World: Europe and America in the Age of Democratic Revolutions (2009), 17, at 28–30CrossRefGoogle Scholar; M. Malia and T. Emmons, History's Locomotives: Revolutions and the Making of the Modern World (2006).

18 M. R. Thompson, Democratic Revolutions: Asia and Eastern Europe (2004), 1–2.

19 A. Khan, ‘A Legal Theory of Revolutions’, (1987) 5 B.U.J. Int’l L. 1, at 2

20 H. Kelsen, Pure Theory of Law, trans (1967), 209.

21 Ibid., at 210. See also Kelsen, supra note 13.

22 Khan, supra note 19, at 2.

23 Ibid.

24 Ibid., at 20.

25 Albert, supra note 2, at 3.

26 Ibid., at 18–23.

27 Ibid., at 7–8, 40.

28 Ibid., at 21.

29 Ibid., at 2.

30 Varol, supra note 2, at 322–45.

31 Ibid., at 295.

32 Therefore, we adopt a broader Kelsenian understanding of revolution which includes coups and other forms of revolution. As to the democratic component, we can retain parts of Varol's definition of democratic coup particularly the requirements that a democratic revolution targets an authoritarian or totalitarian regime and that it responds to popular opposition. See Kelsen, supra note 20, at 209. See also Varol, supra note 2, at 295.

33 This area remains under-theorized, but useful insights that make it appropriate to maintain a distinction between legality and legitimacy in the context of revolutions can be obtained from recent works that attempt to theorize the relationship between legality and legitimacy in relation to the related issue of the international use of force. The doctrine of ‘illegal but legitimate’ use of force was notoriously invoked by the International Commission on Kosovo to justify the 1999 NATO intervention in Kosovo which happened without UN authorization. This doctrine was later used by some scholars to justify the 2003 invasion of Iraq. Scholars have also speculated about the possibility that the use of force could be ‘legal but illegitimate’. See Roberts, A. E., ‘Legality vs Legitimacy: Can Uses of Force be Illegal but Justified?’, in Alston, P. and Macdonald, E. (eds.), Human Rights, Intervention, and the Use of Force (2008), 206–8Google Scholar. See also Nijman, J., ‘After “Iraq”: Back to the International Rule of Law? An Introduction to the NYIL 2011 Agora’, (2011) 42 Netherlands Yearbook of International Law 71, at 87Google Scholar; Slaughter, A., ‘An American Vision of International Law?’, (2003) 97 Am. Soc’y Int’l L. Proc. 125–9Google Scholar.

34 Thompson, supra note 18, at 1.

35 Ibid.

36 See Paust, supra note 2.

37 UN General Assembly, Universal Declaration of Human Rights, 10 December 1948, 217 A (III), Preamble.

38 Paust, H. J., ‘The Human Right to Participate in Armed Revolution and Related Forms of Social Violence: Testing the Limits of Permissibility’, (1983) 32 Emory L. J. 545, at 562Google Scholar; See also Paust, supra note 2.

39 Ibid., at 565–6.

40 See J. Castellino, International Law and Self-Determination: The Interplay of the Politics of Territorial Possession with Formulations of Post-Colonial ‘National’ Identity (2000), 22–9.

41 See UN GA Resolution 1514 (XV), 1960.

42 See ibid., at para. 2. See also International Covenant on Civil and Political Rights (1976), Art. 1; International Covenant on Economic Social and Cultural Rights (1976), Art. 1.

43 See Declaration on Principles of International Law concerning Friendly Relations and Co-operation among States in accordance with the Charter of the United Nations, A/Res/25/2625, 1970.

44 See UN GA Resolutions 2649 (XXV) 1970, 2787 (XXVI) 1971, 3070 (XXVIII), 1973, 3382 (XXX), 1975; A/RES/31/34 1976; A/RES/32/14, 1977; A/RES/33/24, 1989; A/RES/34/44, 1979; A/RES/35/35, 1980; A/RES/36/9,1981; A/RES/37/43, 1982; A/RES/38/17, 1983; A/RES/39/17, 1984; A/RES/40/25, 1985; A/RES/41/101, 1986; A/RES/42/95, 1987; A/RES/43/106, 1988; A/RES/44/79, 1989; A/RES/45/130, 1990.

45 Organization of African Unity, African Charter on Human and Peoples’ Rights, 27 June 1981, CAB/LEG/67/3 rev. 5, 21 ILM 58 (1982), Arts. 20 (2) and (3).

46 Shaw, M. N., ‘Self-Determination and the Use of Force’, in Ghanea-Hercock, N. et al. (eds.), Minorities, Peoples and Self-Determination: Essays In Honour Of Patrick Thornberry (2005), 41Google Scholar.

47 In Re Secession of Quebec, the Canadian Supreme Court held that: ‘International law contains neither a right of unilateral secession nor the explicit denial of such a right.’ Re Secession of Quebec [1998] 2 SCR 217 at para. 112. See also Franck, T., ‘Opinion Directed at Question 2 of the Reference’, in Bayefsky, A. (ed.), Self-Determination in International Law: Quebec and Lessons Learned (2000), at 83Google Scholar.

48 Franck, T., ‘Postmodern Tribalism and the Right to Secession’, in Brölmann, C.et al (eds.), Peoples and Minorities in International Law (1993), at 13Google Scholar.

49 Arbitration Between Great Britain and Costa Rica (1924) 18 AJIL 147.

50 Ibid., at 154.

51 M. N. Shaw, International Law (2008), 454–7.

52 See Murphy, S. D., ‘Democratic Legitimacy and the Recognition of States and Governments’, in Fox, G. H. and Roth, B. R. (eds.), Democratic Governance and International Law (2000), at 139Google Scholar.

53 K. Marek, Identity and Continuity of States in Public International Law (1968), 57.

54 See Franck, supra note 47, at 78.

55 See Okafor, O. C., ‘The Concept of Legitimate Governance’ (1997) 44 NILR 33, at 43–60CrossRefGoogle Scholar. See also W. M. Reisman, ‘Sovereignty and Human Rights in Contemporary International Law’, in Fox and Roth (eds.), supra note 52, at 244–58.

56 Resolution 39/2, inter alia, reads: ‘. . . only the total eradication of apartheid and the establishment of a non-racial democratic society based on majority rule, through the full and free exercise of adult suffrage by all the people in a united and unfragmented South Africa, can lead to a just and lasting solution of the explosive situation in South Africa’. Situation in South Africa, GA Res. 39/2, A/Res/39/2, 1984, at 6.

57 Military and Paramilitary Activities in and against Nicaragua (Nicaragua v. United States of America), Merits, Judgment of 27 June 1986, [1986] ICJ Rep. 1986, at para. 205.

58 For instance, Resolution 45/150 reads: ‘. . . the principle of periodic and genuine elections should not call into question each State's sovereign right freely to choose and develop its political, social, economic, and cultural systems, whether or not they conform to the preferences of other States’. Enhancing the effectiveness the principle of periodic and genuine elections, GA Res 45/150, A/RES/45/150 (1990), at 4. Further, Resolution 45/151 reads: ‘. . . there is no single political system or single model for electoral processes equally suited to all nations and their peoples, and that political systems and electoral processes are subject to historical, political, cultural and religious factors.’ Respect for the principles of national sovereignty and non-interference in the international affairs of states in their electoral processes, GA Res 45/151, A/RES/45/151 (1990), preamble para. 8.

59 Schraeder, P. J., ‘Making the World Safe for Democracy?’, in Schraeder, P. J. (ed.) Exporting Democracy: Rhetoric vs. Reality (2002), at 219–20Google Scholar.

60 See Tusalem, R. F., ‘The United Nations and Democracy Promotion: Assessing the Effectiveness of the UN's Democracy Fund and Electoral Assistance Division’, in Peksen, D. (ed.), Liberal Interventionism and Democracy Promotion (2012), at 177–84Google Scholar. See also K. Samuels, Political Violence and the International Community: Developments in International Law and Policy (2007), 118–20.

61 See SC Res 940, S/RES/940 (1994).

62 See T. Meron, The Humanization of International Law (2006), 314.

63 See SC Res 1132, S/RES/1132 (1997), at 1. See also SC Res 1156, S/RES/1156 (1998), at para 1.

64 See SC Res 1975, S/RES/1975 (2011).

65 Franck, T., ‘The Emerging Right to Democratic Governance’ (1992) 86 AJIL 46, at 46–91CrossRefGoogle Scholar. For a comprehensive introduction to the scholarly debate surrounding the recognition of ‘democratic entitlement’ under international law, see Fox and Roth (eds.), supra note 52. See also Pippan, C., ‘Democracy as a Global Norm: Has it Finally Emerged?’, in Happold, M. (ed.), International Law in a Multipolar World (2011), at 203–23Google Scholar.

66 See D’Aspremont, J., ‘Legitimacy of Governments in the Age of Democracy’, (2006) 38 NYU J. Int’l L. and Pol. 877, at 888Google Scholar.

67 Fox and Roth, ‘Introduction: The Spread of Liberal Democracy and Its Implications for International Law’, in Fox and Roth (eds.), supra note 52, at 11–12. See also W. M. Reisman, ‘Sovereignty and Human Rights in Contemporary International Law’, in Fox and Roth (eds.), supra note 52, at 257–8; Farer, T. J., ‘The Promotion of Democracy: International Law and Norms’, in Newman, E. and Rich, R. (eds.), The UN Role in Promoting Democracy: Between Ideals and Reality (2004), at 55Google Scholar.

68 Reisman, W. M., ‘Why Regime Change is (Almost Always) a Bad Idea’, (2004) 98 AJIL 516, at 517CrossRefGoogle Scholar.

69 See G. Wilson, ‘The United Nations Security Council, Libya and Resolution 1973: Protection of Civilians or Tool for Regime Change?’, in Panara and Wilson (eds.), supra note 2, at 101–22. See also Kuperman, A. J., ‘NATO's Intervention in Libya: A Humanitarian Success?’, in Hehir, A. and Murray, R. (eds.), Libya, the Responsibility to Protect and the Future of Humanitarian Intervention (2013), at 191–221CrossRefGoogle Scholar.

70 For a detailed discussion on the doctrine of Responsibility to Protect, see Section 5.3., infra.

71 For instance a draft resolution on Syria that would have required regime change was supported by the majority of members of the Security Council although the draft failed because of a double veto by Russia and China. See ‘Draft of Security Council Resolution on Syria, The New York Times (31 January 2012), available at <www.nytimes.com/2012/02/01/world/middleeast/draft-of-security-council-resolution-on-syria.html?pagewanted=allamp;&_r&#x003D;0>;. See also J. Vidmar, ‘Human Rights, Democracy and the Legitimacy of Governments in International Law: Practice of States and UN Organs’, in Panara and Wilson (eds.), supra note 2, 70–1.

72 Samuels, supra note 60, at 215.

73 Ibid., at 117.

74 Charter of the Organization of African Unity, 479 UNTS 39, entered into force 13 September 1963, Art. 2.

75 C. A. Odinkalu, ‘Concerning Kenya: The Current AU Position on Unconstitutional Changes in Government’, Open Society Justice Initiative (January 2008) available at <www.afrimap.org/english/images/paper/AU&UnconstitutionalChangesinGovt_Odinkalu_Jan08.pdf>.

76 Ibid.

77 Organization of African Unity (OAU), Declaration on the Framework for an OAU Response to Unconstitutional Changes of Government (AHG/Decl.5 (XXXVI), July 2000.

78 For a comprehensive assessment of the AU's policy of humanitarian intervention, see G. A. Aneme, A Study of the African Union's Right of Intervention against Genocide, Crimes against Humanity and War Crimes (2011).

79 Organization of African Unity (OAU), Constitutive Act of the African Union, OAU Doc.CAB/LEG23.15, 11 July 2000, Art. 4(p) and Art. 30, available at <www.au.int/en/sites/default/files/Constitutive_Act_en_0.htm>.

80 See Kale, N. K., ‘Participatory Rights in Africa: A Brief Overview of an Emerging Regional Custom’, (2008) 55 Neth. Int’l L. Rev. 233 at 235, 239–43Google Scholar.

81 Although the Lomé Declaration is not a legally binding instrument, it nonetheless has legal significance owing to its incorporation under the 2003 Protocol establishing the Peace and Security Council (PSC), the AU's principal organ for peace and security matters including unconstitutional changes of government. For instance, Art. 7(g) of the Protocol empowers the PSC to institute sanctions whenever an unconstitutional change of government takes place as provided for in the Lomé Declaration. See Vandeginste, S., ‘The African Union, Constitutionalism, and Power Sharing’, (2013) 57 Journal of African Law 1CrossRefGoogle Scholar, at 4.

82 African Union (AU), African Charter on Democracy, Elections and Governance, adopted by the eighth ordinary session of the Assembly, Addis Ababa, Ethiopia, 30 January 2007, entered into force 15 February 2012. Other regional instruments which, in one way or another, contribute to the normative content of the African Union's standards of democratic governance include: the African Charter on Human and Peoples’ Rights (1981/1986), the Declaration on the Principles Governing Democratic Elections in Africa (2002), the NEPAD Declaration on Democracy, Political, Economic, and Corporate Governance (2002), and the Protocol relating to the Establishment of the Peace and Security Council of the African Union (2003), and the AU Solemn Declaration on the African Common Defence and Security Policy (2004).

83 Constitutional Rights Project and Civil Liberties Organisation v. Nigeria (2000) AHRLR 191, 198, paras. 50–3 (ACHPR 1998). See also Sir Jawara, Dawda K. v. The Gambia (2000) AHRLR 107, 118 paras. 71–3 (ACHPR 2000)Google ScholarPubMed.

84 Lomé Declaration, paras. 12–15.

85 African Democracy Charter, Art. 25.

86 For an assessment of the achievements of the AU and sub-regional organizations in enforcing the principle of unconstitutional changes of government, see Levitt, J. I., ‘Pro-democratic Intervention in Africa’, (2006–2007) 24 Wis. Int’l L.J. 785Google Scholar. See also Omorogbe, E. Y., ‘A Club of Incumbents? The African Union and Coups d’Etat’, (2011) 44 Vand. J. Transnat’l L. 123Google Scholar.

87 Souaré, I. K., ‘The African Union as A Norm Entrepreneur on Military Coups d’état in Africa (1952–2012): An Empirical Assessment,’ (2014) 52 Journal of Modern African Studies 69, at 86CrossRefGoogle Scholar.

88 See Abass, A., ‘African Regional Organizations, the African Peace and Security Architecture and the Protection of Human Rights’, in Abass, A. (ed.), Protecting Human Security in Africa (2011), 280Google Scholar.

89 African Democracy Charter, Art. 23

90 See F. N. Ikome, ‘Good Coups and Bad Coups: The Limits of the African Union's Injunction on Unconstitutional Changes of Power in Africa’, Institute for Global Dialogue, Occasional Paper No. 55, Johannesburg, South Africa, February 2007. See also Souaré, supra note 87, at 78–9.

91 Ibid.

92 See Abass, supra note 88, at 278.

93 Sturman, K. and Hayatou, A., ‘The Peace and Security Council: From Design to Reality’, in Engel, U. and Porto, J. G. (eds.), Africa's New Peace and Security Architecture: Promoting Norms, Institutionalizing Solutions (2010), 72Google Scholar.

94 Sturman, supra note 10.

95 Burchill, R., ‘The Developing International Law of Democracy’, (2001) 64 Modern Law Review 123CrossRefGoogle Scholar, at 125.

96 This is based on D’Aspremont's theory of legitimacy making a distinction between legitimacy of origin and legitimacy of exercise. See D’Aspremont, supra note 66, at 894–909.

97 See section 5.2., infra.

98 For analysis of the positive impact of elections to democratization in the African context, see S. I. Lindberg, Democracy and Elections in Africa (2006).

99 See Udombana, N. J., ‘Can the Leopard Change its Spots? The African Union Treaty and Human Rights’, (2002) 17 Am. U. Int’l L. Rev 1177, at 1,239–61Google Scholar. See also Murray, R., Human Rights in Africa: From the OAU to the African Union (2004) 23, 48, 56–9Google Scholar.

100 See Kingah, S. S., ‘The African Union's Capacity in Promoting Good Governance’, (2006) 3 Int’l Org. L. Rev. 317, at 329–30Google Scholar. See also Abass, supra note 88; J. S. Omotola, ‘Unconstitutional Changes of Government in Africa: What Implications for Democratic Consolidation?’, Discussion Paper 70, Nordiska Afrikainstitutet (Uppsala 2011) available at <nai.diva-portal.org/smash/get/diva2:478511/FULLTEXT01.pdf>.

101 See AU PSC, Communiqué PSC/AHG/COMM(CCLIX), 28 January 2011; AU PSC, Communiqué PSC/AHG/COMM.1(CCLXV), 10 March 2011; AU PSC, Communiqué PSC/PR/BR.1(CCLXX), 5 April 2011.

102 African Charter on Human and Peoples Rights, supra note 52, Art. 13.

103 See supra note 83.

104 See, e.g., Organization of African Unity (OAU), Declaration on the Principles Governing Democratic Elections in Africa, AHG/Decl. 1 (XXXVIII), 8 July 2002, Arts. 2 and 3; see also African Democracy Charter Arts. 2(3), 3(4), and 17, and The New Partnership for Africa's Development (NEPAD), Declaration on Democracy, Political, Economic and Corporate Governance, AHG/235 (XXXVIII), 18 June 2002, para. 13.

105 Ibid.

106 African Democracy Charter, Arts. 17(4), 23(4) and 25.

107 African Democracy Charter, Art. 23(5). See also Abass, supra note 88, at 278. For a comprehensive assessment of the incorporation of presidential term limits in African constitutions and their significance to constitutionalism, see Fombad, C. M. and Inegbedion, N. A., ‘Presidential Term Limits and Their Impact on Constitutionalism in Africa’, in Fombad, C. M. and Murray, C. (eds.), Fostering Constitutionalism in Africa (2010), 1–183Google Scholar. Out of the 54 member states of the AU, 36 countries have so far incorporated presidential term limits in their constitutions: see I. Souaré, ‘Presidential Term Limits as a Policy Area to Bridge Between the African Union's Security and Governance Norms, abstract available at <www.nomadit.co.uk/ecas/ecas2013/panels.php5?PanelID=1803>. See also H. K. Prempeh, ‘Presidents Untamed’, in Diamond, L. J. and Plattner, M. F. (eds.), Democratization in Africa: Progress and Retreat (2010), 19Google Scholar.

108 African Charter on Human and Peoples’ Rights, supra note 45, Arts. 10, 11, and 13.

109 International Commission on Intervention and State Sovereignty (ICISS), Responsibility to Protect: Report of the International Commission on Intervention and State Sovereignty (2001), available at <idl-bnc.idrc.ca/dspace/bitstream/10625/18432/6/IDL-18432.pdf>. The ICISS Report describes the legal status of the principle as an ‘emerging guiding principle’ of international law supported by ‘growing state and regional organization practice’. Core elements of the principle have been endorsed by the 2005 World Summit of the General Assembly and Security Council Resolution No. 1674. See ICISS Report (2001), at 2.24. See also The 2005 World Summit Outcome Document adopted by the General Assembly, G.A. Res. A/Res/60/1, 16 September 2005, paras. 138, 139; S.C. Res. 1674 (2006), S/Res/1674, 28 April 2006.

110 ICISS Report (2001), at 2.29.

111 Ibid.

112 Ibid., at 2.25.

113 Ibid., at 4.19.

114 Ibid., at 6.1–6.40.

115 United Nations Security Council Resolution No. 1973, The Situation in Libya, S/RES/1973, 17 March 2011.

116 See Wilson, supra note 69. See also Pippan, C., ‘The 2011 Libyan Uprising, Foreign Military Intervention, and International Law’, (2011) 2 Juridikum Zeitschrift für Kritik, at 164–8Google Scholar.

117 See O. Tungwarara, ‘The Arab Spring and the AU Response’, Open Society Institute, Africa Governance Monitoring & Advocacy Project (AfriMAP, 19 September 2011), available at <http://www.afrimap.org/english/images/paper/AfriMAP_NAfrica_Tungwarara_EN.pdf>.

118 See Dersso, S. A., ‘The Quest for Pax Africana: The Case of the African Union's Peace and Security Regime’, (2012) 12 Afr. J. Conf. Res. 11–44Google Scholar. See also Majinge, C. R., ‘The Future of Peacekeeping in Africa and the Normative Role of the African Union’, (2010) 2 Goettingen Journal of International Law 463Google Scholar, at 490–1.

119 AU PSC, Communiqué, PSCPR/COMM.(CCLXI), 23 February 2011.

120 See Sobers, O. H., ‘The Inter-American System of Human Rights’ in Zyberi, G. (ed.), An Institutional Approach to the Responsibility to Protect (2013), 461–2Google Scholar.

121 ICISS Report (2001), at 4.33.

122 Hoffmann, J. and Nollkaemper, A., ‘Concluding Observations’, in Hoffmann, J. and Nollkaemper, A. (eds.), Responsibility to Protect: From Principle to Practice (2012), 368–9Google Scholar.