The Weierstrassian function (p (u) is defined as 
= -;E7> 10 g <’•(“>; 
or, what is the same thing, we have 
P ( u ) = ~ 
d a' (u) 
. . 1 da (A/m) 
But from the equation \/k sn u = ^ ^, we obtain 
and consequently 
du H ('u) 
co A 2 r KJ A 2 sn 2 u ’ 
where, on the right-hand side, expanding in ascending powers of u, the constant term is 
But in the function (Au) this constant term is = 0, and we thus have 
and then, since 
we have