### solve(x) does not fully isolate x. How can I help along?

This is my worksheet.
https://cocalc.com/share/f7766c5e-2f4d-4916-bb0d-74a7182e5fd5/2019-02-09-203517.sagews?viewer=share

In line 50 i solve the equation describing my physical model for d_k:

```
d = solve(p_ges == p_ges_rhs, d_k)
```

But it turns out, that this does not fully isolate d_k at all. Many occurances of d_k remain. How can I help sage along? I really would like to get this fully solved for d_k.

Update: I tried to

```
assume(d_e >0, d_k > d_m > 0, e_m > e_s > 0)
```

things about the equation, but to no avail. In Mathematica `assume()`

is just for simplifying quations, is it the same in sage, with no effect on `solve()`

?

Update2:

I did this:

```
sage: import sympy
sage: x,d_e, d_m, e_m, e_s, v_ges, d_k =var('x d_e d_m e_m e_s v_ges d_k')
sage: sympy.solve(-1/((d_e - x)*e_m) + 1/(e_m*x) + 1/(sqrt((d_e - x)^2 + 4*d_k^2)*d_k*(e_m/d_m + e_s/(d_k - d
....: _m))) - 1/(sqrt(4*d_k^2 + x^2)*d_k*(e_m/d_m + e_s/(d_k - d_m)))-v_ges ,d_k)
[]
sage:
```

which I found mention of here:
https://ask.sagemath.org/question/23967/solve-for-variable-but-variable-is-still-in-answer/

I guess that means there is no solution for that problem. On IRC I was told that it is highly likely true, if sympy says so. doh.