§
Flat functions
Define
f
(
x
)
≡
{
0
x
=
0
e
−
1
/
x
2
x
≠
0
f(x) \equiv \begin{cases} 0 & x = 0 \\ e^{-1/x^2} & x \neq 0 \end{cases}
f
(
x
)
≡
{
0
e
−
1
/
x
2
x
=
0
x
=
0
-
Flat functions on wikipedia