1 | initial version |

Suppose your 3-form is `tau`

; to extract the integrand, simply use `tau[1,2,3].expr()`

, or `tau[frame,1,2,3,chart].expr()`

if the vector frame and the chart are not the default ones on the manifold. Note that `expr()`

returns a symbolic expression, which can be passed directly to `integrate`

. For instance, for the example of question 41228, this would be

```
sage: tau.display(spherical.frame(), spherical)
tau = rho^2*sin(theta) drho/\dtheta/\dphi
sage: tau[spherical.frame(),1,2,3,spherical].expr()
rho^2*sin(theta)
```

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