
where G is a nonempty regular bounded domain in R n and / is a real interval containing zero. The functions a,/, Ai$, &»-, B it c, and C are assumed to be real-valued and continuous on G XI, and the matrices (a,7) and C4*y) symmetric and positive definite in G XI.
A Sturmian theorem has the following form: If (1) has a nontrivial solution u which vanishes identically on the boundary of G and if (2) majorizes (1) in some sense, then every solution v of (2) has a zero in G (or G).
The linear selfadjoint case (bi= z Bi = 0 f i = l, • • • , ti) was first considered by Picone [12] , and later independently and more generally by Hartman and Wintner [4] 

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