@article {14153,
	title = {The Optimal Warranty and Preventive Maintenance Policy for the Four-State System},
	year = {2011},
	attachments = {https://scholar.cu.edu.eg/sites/default/files/medial_sector/files/03_2.pdf},
	author = {Ahmed F. Attia and Eman D. Abou Elela and Hany A. Hosham}
}
