@article {MR957652,
	title = {Existence of an optimal {M}arkovian filter for the control under partial observations},
	journal = {SIAM J. Control Optim.},
	volume = {26},
	number = {5},
	year = {1988},
	pages = {1025{\textendash}1061},
	issn = {0363-0129},
	doi = {10.1137/0326057},
	url = {http://db.lic.vnu.edu.vn:2080/10.1137/0326057},
	author = {El Karoui, Nicole and Nguyen Huu Du and Jeanblanc-Picqu{\'e}, Monique}
}
