\begin{definition}[Definition:Conjugate Point (Calculus of Variations)/wrt original Functional]
Let:
:$\ds \int_a^b \map F {x, y, y'}$
be the original functional.
Let $\tilde a$ be conjugate to $a$.
Let:
:$\ds \int_a^b \paren {P h'^2 + Q h^2} \rd x$
be the second variation of $\ds \int_a^b \map F {x, y, y'}$.
Then $\tilde a$ is '''conjugate''' to $a$ {{WRT}} to the original functional $\ds \int_a^b \map F {x, y, y'}$.
{{explain|What exactly is meant by "original functional"?}}
\end{definition}