Excuse me sir!...

... explain me please what is the difference in the two cases...

a) $\displaystyle u = \frac {e^{x\cdot y}}{1+x} + c \cdot e^{-y} $ where $\displaystyle x$ and $\displaystyle c$ are two constants independent from $\displaystyle y$

b) $\displaystyle u = \frac {e^{x\cdot y}}{1+x} + f(x) \cdot e^{-y} $ where $\displaystyle x$ is an arbitrary constant independent from $\displaystyle y$ and $\displaystyle f(x)$ is an arbitrary function of the constant $\displaystyle x$

... a little mysterious question

...

Kind regards

$\displaystyle \chi$ $\displaystyle \sigma$