Hello! I have the following function

```
using SpecialFunctions
function CDFFoldedNormal(x,μ,σ)
#follow the example: https://en.wikipedia.org/wiki/Folded_normal_distribution
#Note that the folded normal is NOT the half normal (unless μ=0)
term1 = erf((x+μ)/(sqrt(2)*σ));
term2 = erf((x-μ)/(sqrt(2)*σ));
return 0.5 * (term1 + term2);
end
```

which is part of the following function that is supposed to modify its argument:

```
function foo!(F,x)
F = CDFFoldedNormal(x,0.03,0.05) - 0.95;
end
```

When I try to evaluate the function that modifies its argument in-place, like so

```
F = 0.
foo!(F,0.105)
```

Instead of getting `F`

as a modified argument. I get F as a redefined function and the error message `invalid redefinition of constant Main.F `

Could someone please help me rewrite the function `foo!`

so that it modifies its argument in-place?

Thank you!