(NoBYKNOWENNYE DIFFERENCIALXNYE URAWNENIQ I OSNOWY WARIACIONNOGO IS^ISLENIQs - (NkARTA[EW a(B.(Np(B., (NrOVDESTWENSKIJ b(B.(Nl(B.s ((NmOSKWAs (NnAUKAs, 1980)