Darajat, P.P. et al. 2023. Dynamical Analysis and Optimal Control of SVIR Hepatitis B Model Spread in Malang. Vygotsky: Jurnal Pendidikan Matematika dan Matematika. 5, 2 (Aug. 2023), 77–90. DOI:https://doi.org/10.30736/voj.v5i2.698.