@_Maxim_ 

Thank you very much

@Markiyan Hirnyk 

But, in short, I think I know this....
But Maple, in all the examples I have had him carry out, always writes y0 and x0 with the same sign and in the same member. Instead, in all the texts and also in Wolfram's quoted site, the curve equation in the form of
Weierstrass always starts with y^2 = x^3+..., i. e. y^2 and x^3 have a +1 coefficient.

@Markiyan Hirnyk 

I apologise if I still ask for explanations. So I have to interpete

x0^3 - 7*x0 + 88 +y0^2; as

y0^2= x0^3-7*x0+88 ?

Thank you very much

@Markiyan Hirnyk 

No, because I asked how the writing of the curve equation should be interpreted and not an explanation of the theory of elliptical curves.

@Markiyan Hirnyk 

It seems to me that you have not answered my question