Learn how to do simple math with C#.
Learn how to separately compile a function into a library and then link it to your Main function.

Calculate (using System.Math class) √2, 2^1/5, e^π, π^e.
Check that the results are correct, something like
```
double sqrt2=Sqrt(2.0);
Write($"sqrt2^2 = {sqrt2*sqrt2} (should equal 2)\n");
```
Using the following Stirling approximation for the gamma-function Γ(x),
```
static double gamma(double x){
///single precision gamma function (formula from Wikipedia)
if(x<0)return PI/sin(PI*x)/gamma(1-x); // Euler's reflection formula
if(x<9)return gamma(x+1)/x; // Recurrence relation
double lngamma=x*Log(x+1/(12*x-1/x/10))-x+Log(2*PI/x)/2;
return Exp(lngamma);
}
```
calculate Γ(1), Γ(2), Γ(3), Γ(10). Check that the results are correct (within single precision: about 6 decimal digits).

You should put your gamma function in a static class "sfuns" (special functions) in a file "sfuns.cs", compile it separately into a library, and then link to your Main function.
The gamma-function overflows very easily, so the logarithm of the gamma function, lngamma, is often a more useful function. Figure out how to modify the above formula to calculate lngamma. For simplicity you should only allow positive arguments for your lngamma:
```
if(x <= 0) return double.NaN;
if(x < 9) return lngamma(x+1) - Log(x);
```

In the Makefile you should redirect the output of your program to an output file for me to see it,
```
Out.txt: main.exe
	mono main.exe > Out.txt
```
You compile a piece of source code, say "sfuns.cs", into a library, say "sfuns.dll", like this,
```
sfuns.dll : sfuns.cs
	mcs -target:library -out:sfuns.dll sfuns.cs 
```

You link your library to your "main.cs" like this,

main.exe : main.cs sfuns.dll
	mcs -target:exe -out:main.exe -reference:sfuns.dll main.cs