Home Financial crisis spread, economic growth and unemployment: a mathematical model
Article
Licensed
Unlicensed Requires Authentication

Financial crisis spread, economic growth and unemployment: a mathematical model

  • Calvin Tadmon ORCID logo EMAIL logo and Eric Rostand Njike Tchaptchet
Published/Copyright: April 21, 2022

Abstract

The unemployment is the main channel through which the economic and financial crises influence the social development. In this paper, we propose a mathematical model to study the interactions between financial crisis spread, economic growth and unemployment. We also solve an optimal control problem focusing on the minimization, at the lowest cost, of the adverse effects of the financial crisis. The analysis of the model leads us to two equilibria: (1) a stress free equilibrium, where the economy and the employment are optimal, and (2) a stressed equilibrium. We obtain a theoretical confirmation of Okun’s law and a formula to compute the minimum reservation wage in terms of model parameters. Numerical simulations are performed to illustrate the theoretical results obtained.


Corresponding author: Calvin Tadmon, Department of Mathematics and Computer Science, University of Dschang, Dschang, Cameroon, E-mail:

  1. Author contribution: All the authors have accepted responsibility for the entire content of this submitted manuscript and approved submission.

  2. Research funding: None declared.

  3. Conflict of interest statement: The authors declare that they have no conflict of interest.

Proof

Proposition 1

  1. Let t ≥ 0.

From the first equation of (21), we have

d ( t ) = d ( 0 ) exp 0 t ( θ 0 k σ ( s ) g ) ( 1 d ( s ) ) ξ b d s 0 .

From the second equation of (21), we have

τ ( t ) = τ ( 0 ) exp 0 t ϕ ( u ) d u > 0 ,

where ϕ ( u ) = α α + μ ( ρ + η + δ ) λ 0 1 d ( u ) ε ( 1 α ) ( 1 ν ) β 1 α α τ ( 1 α ) μ α ( u ) .

From the third equation of (21), we have

k ( t ) = k ( 0 ) exp 0 t λ 0 1 d ( u ) ε k α 1 ( u ) τ 1 α ( u ) ( δ + ρ + η ) d u > 0 .
  1. The positivity of h(t) can easily be proved. From the relation h(t) + d(t) = 1, we deduce that 0 ≤ d(t) ≤ 1.

From the first equation of (21) and the positivity of τ, we have

( 1 α ) μ α τ ( 1 α ) μ α 1 ( t ) τ ̇ ( t ) = ( 1 α ) μ α + μ ( ρ + η + δ ) τ ( 1 α ) μ α λ 0 ( 1 d ( t ) ) ε ( 1 α ) ( 1 ν ) β 1 α α .

That is

d d t τ ( 1 α ) μ α ( t ) = ( 1 α ) μ α + μ ( ρ + η + δ ) τ ( 1 α ) μ α λ 0 ( 1 d ( t ) ) ε ( 1 α ) ( 1 ν ) β 1 α α < ( 1 α ) μ α + μ ( ρ + η + δ ) τ ( 1 α ) μ α + λ 0 ( 1 α ) μ α + μ ( 1 α ) ( 1 ν ) β 1 α α .

Therefore,

τ ( 1 α ) μ α ( t ) λ 0 ρ + η + δ ( 1 α ) ( 1 ν ) β 1 α α + τ ( 1 α ) μ α ( 0 ) λ 0 ρ + η + δ ( 1 α ) ( 1 ν ) β 1 α α e ( 1 α ) μ ( ρ + η + δ ) α + μ t .

If τ ( 0 ) λ 0 ρ + η + δ α ( 1 α ) μ ( 1 α ) ( 1 ν ) β 1 μ , then

lim sup t τ ( 1 α ) μ α ( t ) = λ 0 ρ + η + δ ( 1 α ) ( 1 ν ) β 1 α α

and

(31) τ ( t ) λ 0 ρ + η + δ α ( 1 α ) μ ( 1 α ) ( 1 ν ) β 1 μ .

From the second equation of (21) and the positivity of k, we have

( 1 α ) k α ( t ) k ̇ ( t ) = ( 1 α ) λ 0 ( 1 d ( t ) ) ε τ 1 α ( t ) ( 1 α ) ( ρ + η + δ ) k 1 α ( t ) .

That is,

(32) d d t k 1 α ( t ) = ( 1 α ) λ 0 ( 1 d ( t ) ) ε τ 1 α ( 1 α ) ( ρ + η + δ ) k 1 α ( t ) .

Using (31), (32) becomes

(33) d d t k 1 α ( t ) ( 1 α ) λ 0 ( 1 d ( t ) ) ε λ 0 ρ + η + δ α μ ( 1 α ) ( 1 ν ) β 1 μ ( 1 α ) ( ρ + η + δ ) k 1 α ( t ) .

Since d(t) ≤ 1, (33) becomes

d d t k 1 α ( t ) ( 1 α ) λ 0 λ 0 ρ + η + δ α μ ( 1 α ) ( 1 ν ) β 1 α μ ( 1 α ) ( ρ + η + δ ) k 1 α ( t ) .

That is,

k 1 α ( t ) λ 0 ρ + η + δ α + μ μ ( 1 α ) ( 1 ν ) β 1 α μ + k ( 0 ) 1 α λ 0 ρ + η + δ α + μ μ ( 1 α ) ( 1 ν ) β 1 α μ e ( 1 α ) ( ρ + η + δ ) t .

If k ( 0 ) λ 0 ρ + η + δ ( α + μ ) ( 1 α ) μ ( 1 α ) ( 1 ν ) β 1 μ , then

lim sup t k 1 α ( t ) = λ 0 ρ + η + δ α + μ μ ( 1 α ) ( 1 ν ) β 1 α μ

and k ( t ) λ 0 ρ + η + δ ( α + μ ) ( 1 α ) μ ( 1 α ) ( 1 ν ) β 1 μ .□

Proof

Proposition 2

Consider the function Φ defined from 0 , × ( 0 , ) 2 to 0 , × ( 0 , ) 2 by

Φ ( d , τ , k ) = d ( θ 0 k σ ( t ) g ) ( 1 d ) ξ b α α + μ ρ + η + δ λ 0 ( 1 d ) ε ( 1 α ) ( 1 ν ) β 1 α α τ ( 1 α ) μ α τ λ 0 ( 1 d ) ε k α τ 1 α ( δ + ρ + η ) k .

Φ is a continuously differentiable function on 0 , × ( 0 , ) 2 ; hence it is locally Lipschitz. From the Cauchy–Lipschitz Theorem (Liao, Wang, and Yu 2007), problem (21) admits a unique local solution. From Proposition 1, the solution is contained in a compact subset of R 3 . Therefore it is globally defined. □

Proof

Proposition 3

We assume that β ( 1 α ) ( 1 ν ) λ 0 ρ + η + δ α ( 1 α ) .

Let t ≥ 0. From Proposition 1, we have

(34) τ ( t ) λ 0 ρ + η + δ α ( 1 α ) μ ( 1 α ) ( 1 ν ) β 1 μ .

Therefore, if β ( 1 α ) ( 1 ν ) λ 0 ρ + η + δ α ( 1 α ) , then

λ 0 ρ + η + δ α ( 1 α ) μ ( 1 α ) ( 1 ν ) β 1 μ 1

and τ(t) ≤ 1. □

Proof

Proposition 4

A point (d, τ, k) is an equilibrium of (21), if it is a solution of the following system

(35) d θ 0 k σ g ( 1 d ) ξ b = 0 , α α + μ ρ + η + δ λ 0 ( 1 d ) ε ( 1 α ) ( 1 ν ) β 1 α α τ ( 1 α ) μ α τ = 0 , λ 0 ( 1 d ) ε k α τ 1 α ( δ + ρ + η ) k = 0 .

From the second and third equations of (35), we obtain

(36) τ = λ 0 ρ + η + δ α ( 1 α ) μ ( 1 α ) ( 1 ν ) β 1 μ ( 1 d ) α ε ( 1 α ) μ

and

(37) k = λ 0 ρ + η + δ α + μ μ ( 1 α ) ( 1 α ) ( 1 ν ) β 1 μ ( 1 d ) ε ( α + μ ) μ ( 1 α ) .

Using (36), (37) and following the same development as in Bucci et al. (2019), we obtain the result. □

Proof

Proposition 5

The Jacobian matrix J(d, τ, k) of (21) is defined by

(38) J ( d , τ , k ) = J 1 ( d , τ , k ) 0 J 2 ( d , τ , k ) J 3 ( d , τ , k ) J 4 ( d , τ , k ) 0 J 5 ( d , τ , k ) J 6 ( d , τ , k ) J 7 ( d , τ , k ) ,

where

J 1 ( d , τ , k ) = θ 0 k σ g ( 1 2 d ) ξ b ,

J2(d, τ, k) = θ0σd(1 − d)kσ−1,

J 3 ( d , τ , k ) = λ 0 ε α α + μ ( 1 d ) ε 1 ( 1 α ) ( 1 ν ) β 1 α α τ 1 ( 1 α ) μ α ,

J 4 ( d , τ , k ) = α α + μ ρ + η + δ 1 ( 1 α ) μ α λ 0 ( 1 d ) ε ( 1 α ) ( 1 ν ) β 1 α α τ ( 1 α ) μ α ,

J5(d, τ, k) = −λ0ɛ(1 − d)ɛ−1k α τ1−α,

J6(d, τ, k) = (1 − α)λ0(1 − d) ɛ k α τα, and

J7(d, τ, k) = αλ0(1 − d) ɛ kα−1τ1−α − (ρ + η + δ).

  1. At Q 0 * , the eigenvalues of (38) are

    λ 1 = θ 0 λ 0 ρ + η + δ σ ( α + μ ) μ ( 1 α ) ( 1 α ) ( 1 ν ) β σ μ ( ξ + g + b )
    λ 2 = ( 1 α ) μ ( ρ + η + δ ) α + μ and λ 3 = ( α 1 ) ( ρ + η + δ ) .
Since α < 1, it follows that λ2 are λ3 are negative real numbers. Therefore, for Q 0 * to be locally stable, λ1 must be non-positive, that is

θ 0 λ 0 ρ + η + δ σ ( α + μ ) μ ( 1 α ) ( 1 α ) ( 1 ν ) β σ μ ξ + g + b .
  1. Similarly, by using the Routh–Hurwitz criterion, we obtain the local asymptotic stability of Q*.

Proof

Proposition 6

For given value of d = d*, system (21) becomes

(39) τ ̇ ( t ) = α α + μ ρ + η + δ λ 0 ( 1 d * ) ε ( 1 α ) ( 1 ν ) β 1 α α τ ( 1 α ) μ α ( t ) τ ( t ) , k ̇ ( t ) = λ 0 ( 1 d * ) ε k α ( t ) τ 1 α ( t ) ( δ + ρ + η ) k ( t ) .

It is easy to verify that (τ*, k*) is the unique equilibrium of (39).

From the first equation of (39) and the positivity of τ, we have

( 1 α ) μ α τ ( 1 α ) μ α 1 τ ̇ = ( 1 α ) μ α + μ ( ρ + η + δ ) τ ( 1 α ) μ α λ 0 ( 1 d * ) ε ( 1 α ) ( 1 ν ) β 1 α α .

That is

d d t τ ( 1 α ) μ α ( t ) = ( 1 α ) μ α + μ ( ρ + η + δ ) τ ( 1 α ) μ α λ 0 ( 1 d * ) ε ( 1 α ) ( 1 ν ) β 1 α α .

Therefore, for tt0

τ ( 1 α ) μ α ( t ) = λ 0 ( 1 d * ) ε ρ + η + δ ( 1 α ) ( 1 ν ) β 1 α α + τ ( 1 α ) μ α ( t 0 ) λ 0 ( 1 d * ) ε ρ + η + δ ( 1 α ) ( 1 ν ) β 1 α α e ( 1 α ) μ ( ρ + η + δ ) α + μ t .

If τ ( 1 α ) μ α ( t 0 ) λ 0 ( 1 d * ) ε ρ + η + δ ( 1 α ) ( 1 ν ) β 1 α α , that is τ(t0) ≤ τ*, then

lim sup t τ ( 1 α ) μ α ( t ) = λ 0 ( 1 d * ) ε ρ + η + δ ( 1 α ) ( 1 ν ) β 1 α α

and for all tt0, τ(t) ≤ τ*.

If τ(t0) ≥ τ*, then

lim inf t τ ( 1 α ) μ α ( t ) = λ 0 ( 1 d * ) ε ρ + η + δ ( 1 α ) ( 1 ν ) β 1 α α

and for all tt0, τ(t) ≥ τ*.

From the second equation of (39) and the positivity of k, we have

( 1 α ) k α k ̇ ( t ) = ( 1 α ) λ 0 ( 1 d * ) ε τ 1 α ( 1 α ) ( ρ + η + δ ) k 1 α ( t ) .

That is,

d d t k 1 α ( t ) = ( 1 α ) λ 0 ( 1 d * ) ε τ 1 α ( 1 α ) ( ρ + η + δ ) k 1 α ( t ) .

Therefore, for tt0

(40) k 1 α ( t ) = k 1 α ( t 0 ) e ( 1 α ) ( ρ + η + δ ) t + ( 1 α ) λ 0 ( 1 d * ) ε 0 t e ( s t ) ( 1 α ) ( ρ + η + δ ) τ 1 α ( s ) d s .
  1. If τ(t0) ≤ τ*, then from (40) we have the inequality

    (41) k 1 α ( t ) k 1 α ( t 0 ) e ( 1 α ) ( ρ + η + δ ) t + k * 1 α 1 e ( 1 α ) ( ρ + η + δ ) t .

    Additionally if k(t0) ≤ k*, then from (41) we get

    lim sup t k ( t ) = k *
and for all tt0 k(t) ≤ k*.
  1. If τ(t0) ≥ τ*, then from (40) we have the inequality

    (42) k 1 α ( t ) k 1 α ( t 0 ) e ( 1 α ) ( ρ + η + δ ) t + k * 1 α 1 e ( 1 α ) ( ρ + η + δ ) t .

    Additionally if k(t0) ≥ k*, then from (42) we get

    lim inf t k ( t ) = k *

    and for all tt0, k(t) ≥ k*.

Note from (a) and (b) that, if τ(t0) = τ* and k(t0) = k*, there is no further variations of τ and k.

Now, if τ(t0) < τ* and k(t0) < k*, then

λ 0 ( 1 d * ) ε ρ + η + δ τ 1 α ( t 0 ) k 1 α ( t 0 ) < k * 1 α k 1 α ( t 0 ) < 0

and

α τ * ( 1 α ) μ α τ ( 1 α ) μ α ( t 0 ) ( α + μ ) λ 0 ( 1 d * ) ε ρ + η + δ τ 1 α ( t 0 ) k 1 α ( t 0 ) k α ( t 0 ) τ 1 ( 1 α ) μ α ( t 0 ) > 0 .

Proof

Theorem 2

Direct computations show that system (28) follows from the adjoint system of the PMP (Sethi 2018). Similarly, the equalities in (30) are directly given by the transversality conditions of the PMP. It remains to characterize the control using the minimality condition of the PMP (Sethi 2018).

The minimality condition on the set t [ 0 , t f ] : 0 < u * ( t ) < 1 is

H u * = 2 γ 1 u * p 1 d * = 0 .

Thus, on this set,

u * = p 1 d * 2 γ 1 .

If t t [ 0 , t f ] : u * = 1 , then the minimality condition is

H u * = 2 γ 1 u * p 1 d * 0 , i . e , p 1 d * 2 γ 1 1 .

If t t [ 0 , t f ] : u * = 0 , then the minimality condition is

H u * = 2 γ 1 u * p 1 d * 0 , i . e , p 1 d * 2 α 1 0 .

Therefore, we obtain (30). □

References

Adachi, H., S. Imoto, and K. Inagaki. 2015. “Economic Growth and Unemployment: Theoretical Foundation of Okun’s Law.” In Studies in Medium-Run Macroeconomics Growth, Fluctuations, Unemployment, Inequality and Policies, edited by H. Adachi, T. Nakamura, and Y. Osumi, 69–85. Singapore: World Scientific.10.1142/9789814619585_0003Search in Google Scholar

Allen, F., and D. Gale. 2000. “Financial Contagion.” Journal of Political Economy 108 (1): 1–33. https://doi.org/10.1086/262109.Search in Google Scholar

Avakov, E. R. 1988. “The Maximum Principle for Abnormal Optimal Control Problems.” Doklady Akademii Nauk SSSR 298 (6): 1289–92.Search in Google Scholar

Bartolucci, F., M. Choudhry, E. Marelli, and M. Signorelli. 2011. “Financial Crises and Unemployment: Beyond the Okun’s Law.” In Paper presented at Sixteenth World Congress of the International Economic Association. Beijing: Tsinghua University.Search in Google Scholar

Blanchard, O. J. 1997. “The Medium Run.” Brookings Papers on Economic Activity 2: 89–158. https://doi.org/10.2307/2534687.Search in Google Scholar

Bolos, B., V. Bacarea, and M. Marusteri. 2011. “Approaching Economic Issues through Epidemiologyan Introduction to Business Epidemiology.” Romanian Journal of Economic Forecasting 14 (1): 257–76.Search in Google Scholar

Boyko, A., V. Kukartsev, and V. Tynchenko. 2019. “Simulation-Dynamic Model of Long-Term Economic Growth Using Solow Model.” Journal of Physics: Conference Series 1 (1353): 1–6. https://doi.org/10.1088/1742-6596/1353/1/012138.Search in Google Scholar

Brusco, S., and F. Castiglionesi. 2007. “Liquidity Coinsurance, Moral Hazard, and Financial Contagion.” The Journal of Finance 62: 2275–302. https://doi.org/10.1111/j.1540-6261.2007.01275.x.Search in Google Scholar

Bucci, A., D. La Torre, D. Liuzzi, and S. Marsiglio. 2019. “Financial Contagion and Economic Development: An Epidemiological Approach.” Journal of Economic Behavior & Organization 162 (1): 211–28. https://doi.org/10.1016/j.jebo.2018.12.018.Search in Google Scholar

Caballero, R. J., and A. Krishnamurthy. 2008. “Collective Risk Management in a Flight to Quality Episode.” The Journal of Finance 63 (5): 2195–230. https://doi.org/10.1111/j.1540-6261.2008.01394.x.Search in Google Scholar

Caccioli, F., P. Barucca, and T. Kobayashi. 2018. “Network Models of Financial Systemic Risk: A Review.” Journal of Computational Social Science 1 (1): 81–114. https://doi.org/10.1007/s42001-017-0008-3.Search in Google Scholar

Choudhry, M. T., E. Marelli, and M. Signorelli. 2012. “Youth Unemployment Rate and Impact of Financial Crisis.” International Journal of Manpower 33 (1): 76–95. https://doi.org/10.1108/01437721211212538.Search in Google Scholar

Cooper, J. C. 2003. “Price Elasticity of Demand for Crude Oil: Estimates for 23 Countries.” OPEC Review 27 (1): 1–8. https://doi.org/10.1111/1468-0076.00121.Search in Google Scholar

Diamond, D. W., and P. H. Dybvig. 1983. “Bank Runs, Deposit Insurance, and Liquidity.” Journal of Political Economy 91 (3): 401–19. https://doi.org/10.1086/261155.Search in Google Scholar

Farmer, R. E. 2013. “Animal Spirits, Financial Crises and Persistent Unemployment.” The Economic Journal 123 (568): 317–40. https://doi.org/10.1111/ecoj.12028.Search in Google Scholar

Fernández, A., and J. Herreño. 2013. “Equilibrium Unemployment during Financial Crises.” In IADB Working Paper Series, No. IDB-WP-390.10.2139/ssrn.2275156Search in Google Scholar

Fleming, W. H., and R. W. Rishel. 1975. Deterministic and Stochastic Optimal Control. New York: Springer.10.1007/978-1-4612-6380-7Search in Google Scholar

Gai, P., and A. H. S. Kapadia. 2011. “Complexity, Concentration and Contagion.” Journal of Monetary Economics 58 (5): 453–70. https://doi.org/10.1016/j.jmoneco.2011.05.005.Search in Google Scholar

Gaff, H., and E. Schaefer. 2009. “Optimal Control Applied to Vaccination and Treatment Strategies for Various Epidemiological Models.” Mathematical Biosciences and Engineering 6 (3): 469–92. https://doi.org/10.3934/mbe.2009.6.469.Search in Google Scholar PubMed

Ghoshray, A., J. Ordóñez, and H. Sala. 2016. “Euro, Crisis and Unemployment: Youth Patterns, Youth Policies.” Economic Modelling 58: 442–53. https://doi.org/10.1016/j.econmod.2016.05.017.Search in Google Scholar

Glasserman, P., and H. P. Young. 2016. “Contagion in Financial Networks.” Journal of Economic Literature 54 (3): 779–831. https://doi.org/10.1257/jel.20151228.Search in Google Scholar

Inci, O. R., and M. P. Anca. 2013. “The Social Impact of Financial Crises: Evidence from the Global Financial Crisis.” In World Bank Policy Research Working Paper.Search in Google Scholar

Jianu, I. 2019. “The Relationship between the Economic and Financial Crises and Unemployment Rate in the European Union: How Institutions Affected Their Linkage?” Journal of Eastern Europe Research in Business & Economics 53 (2): 1–16. https://doi.org/10.5171/2019.403548.Search in Google Scholar

Kostylenko, O., H. S. Rodrigues, and D. F. M. Torres. 2017. “Banking Risk as an Epidemiological Model: An Optimal Control Approach.” In Springer Proceedings in Mathematics and Statistics, Vol. 223, 165–76.10.1007/978-3-319-71583-4_12Search in Google Scholar

Liao, X., L. Wang, and P. Yu. 2007. “Stability of Dynamical Systems.” In Monograph Series on Nonlinear Science and Complexity, Vol. 5.10.1016/S1574-6917(07)05001-5Search in Google Scholar

Müller, J. 2006. “Interbank Credit Lines as a Channel of Contagion.” Journal of Financial Services Research 29 (1): 37–60. https://doi.org/10.1007/s10693-005-5107-2.Search in Google Scholar

Nagel, K. 2015. “Relationships between Unemployment and Economic Growth - the Review (Results) of the Theoretical and Empirical Research.” Journal of Economics and Management 20: 64–79.Search in Google Scholar

Okun, A. 1962. “Potential GNP: Its Measurement and Significance, American Statistical Association.” In Proceedings of the Business and Economics Statistics Section, 98–103.Search in Google Scholar

Okun, A. 1970. “Potential GDP: Its Measurement and Significance.” In The Political Economy of Prosperity. Washington: Brooking Institution.Search in Google Scholar

Philippas, D., Y. Koutelidakis, and A. Leontitsis. 2015. “Insights into European Interbank Network Contagion.” Managerial Finance 41 (8): 754–72. https://doi.org/10.1108/mf-03-2014-0095.Search in Google Scholar

Sere, K. A., and B. H. M. Tchereni. 2020. “Nonlinear Modelling of Economic Growth and Unemployment in South Africa.” Acta Universitatis Danubius - œconomica 16 (6): 273–82.Search in Google Scholar

Sethi, S. P. 2018. Optimal Control Theory: Applications to Management Science and Economics. Switzerland: Springer.10.1007/978-3-319-98237-3Search in Google Scholar

Solow, R. M. 1956. “A Contribution to the Theory of Economic Growth.” Quarterly Journal of Economics 70 (1): 65–94. https://doi.org/10.2307/1884513.Search in Google Scholar

Soylu, O. B., I. Çakmak, and F. Okur. 2018. “Economic Growth and Unemployment Issue: Panel Data Analysis in Eastern European Countries.” Journal of International Studies 11 (1): 93–107. https://doi.org/10.14254/2071-8330.2018/11-1/7.Search in Google Scholar

Swan, T. W. 1956. “Economic Growth and Capital Accumulation.” The Economic Record 32 (2): 334–61. https://doi.org/10.1111/j.1475-4932.1956.tb00434.x.Search in Google Scholar

Toivanen, M. 2013. “Contagion in the Interbank Network: An Epidemiological Approach.” In Bank of Finland Research Discussion Papers, Vol. 19.10.2139/ssrn.2331300Search in Google Scholar

Viladent, C. 2009. “An Epidemiologic Approach of Financial Markets.” In Globalization and the Reform of the International Banking and Monetary System, 258–65. Switzerland: Springer.10.1057/9780230251069_13Search in Google Scholar

Wagner, W. 2010. “In the Quest of Systemic Externalities: A Review of the Literature.” CESifo Economic Studies 56 (1): 96–111. https://doi.org/10.1093/cesifo/ifp022.Search in Google Scholar


Supplementary Material

The online version of this article offers supplementary material (https://doi.org/10.1515/snde-2021-0081).


Received: 2021-08-19
Accepted: 2022-03-26
Published Online: 2022-04-21

© 2022 Walter de Gruyter GmbH, Berlin/Boston

Downloaded on 17.9.2025 from https://www.degruyterbrill.com/document/doi/10.1515/snde-2021-0081/html
Scroll to top button