yJ = Ct ( * = l , 2 , . . , n ) , (45) with the essential proviso t h a t these equations are soluble with respect t o yv y2, . . , yn- Any equation of set (45) is called an integral of system (42), and n such integrals have to be found t o make u p the general solution of the system; thus it follows t h a t equations (45) must be soluble with respect to yv y2t .
A First Course in Infinitesimal Calculus by Daniel A. Murray