Can someone please give me a helping hand with plot3d?

I want to plot the GammaCondor-function:

```
def condor(x, y):
e = gamma(y+1)
a = gamma(1/2*y-1/2*x+1/2)
b = gamma(-1/2*x+1/2*y+1)
c = gamma(1/2*x+1/2*y+1/2)
d = gamma(1/2*x+1/2*y+1)
alpha = cos(pi*(y-x))
beta = cos(pi*(y+x))
return log(e)+log(a)*((alpha-1)/2)+log(b)*((-alpha-1)/2) \
+log(c)*((beta-1)/2)+log(d)*((-beta-1)/2)
```

With Maple this is easy (note the restriction for x):

```
plot3d(condor(x, y), x = -y..y, y = 0..8,
orientation = [-145, -105], axes = BOXED, grid = [64,64]);
```

What this looks like can be seen here:
http://luschny.de/math/asy/ElCondorYElGamma.html

Or as a dynamic pdf with an Adobe Reader (v10 or later):
http://luschny.de/math/asy/Condor.pdf

```
var('x, y')
g = plot3d(condor(x, y), (x, -y, y), (y, 0, 8))
show(g)
```

gives a TypeError.

```
var('x, y')
g = plot3d(condor(x, y), (x, -8, 8), (y, 0, 8))
show(g)
```

shows an empty frame. Plotting was tried on cloud.sagemath.