Hi, and thanks as always for cdb.

I think I may be missing something, but I can't figure what it might be. Please consider the following two pieces of code; they only differ in that the first uses `canonicalise`

while the second uses `meld`

. However the second gives 0 as the result and I don't see why.

First segment of code:

```
\partial{#}::PartialDerivative.
{\mu,\nu,μ,ν}::Indices(spacetime,position=fixed).
f::Depends(\partial{#}).
\delta_{\alpha}^{\mu}::KroneckerDelta.
{\alpha,\beta,α,β}::Indices(flat,position=fixed).
e_{\alpha}^{\mu}::Depends(\partial{#}).
{u^{\mu},v^{\mu}, \partial_{\nu}{Q??}, \partial_{\nu}{f}, \partial_{\mu\nu}{f}, e_{\nu}, f, (1/f)}::SortOrder.
ex := \partial_{μ}(e_{β}^{ν}) \partial_{ν}(f) e_{α}^{μ} +
\partial_{μ ν}(f) e_{α}^{μ} e_{β}^{ν}
-\partial_{μ}(e_{α}^{ν}) \partial_{ν}(f) e_{β}^{μ}
-\partial_{μ ν}(f) e_{α}^{ν} e_{β}^{μ}.
ex;
canonicalise(ex);
```

Second segment of code:

```
\partial{#}::PartialDerivative.
{\mu,\nu,μ,ν}::Indices(spacetime,position=fixed).
f::Depends(\partial{#}).
\delta_{\alpha}^{\mu}::KroneckerDelta.
{\alpha,\beta,α,β}::Indices(flat,position=fixed).
e_{\alpha}^{\mu}::Depends(\partial{#}).
{u^{\mu},v^{\mu}, \partial_{\nu}{Q??}, \partial_{\nu}{f}, \partial_{\mu\nu}{f}, e_{\nu}, f, (1/f)}::SortOrder.
ex := \partial_{μ}(e_{β}^{ν}) \partial_{ν}(f) e_{α}^{μ} +
\partial_{μ ν}(f) e_{α}^{μ} e_{β}^{ν}
-\partial_{μ}(e_{α}^{ν}) \partial_{ν}(f) e_{β}^{μ}
-\partial_{μ ν}(f) e_{α}^{ν} e_{β}^{μ}.
ex;
meld(ex);
```

Thank you

GPN