I've been trying to make use of `meld`

and I'm finding some potential bugs.

Consider:

`X_{a b c}_{d}::TableauSymmetry(shape=(2,1,1), indices=(0,3,1,2)).`

This generates a tensor `X_{a b c}_{d}`

which is antisymmetric in `abc`

but with the totally antisymmetric part in `abcd`

removed.

If I evaluate meld on the following three quantities:

```
meld($ X_{a b d d}$);
meld($ X_{a d b d}$);
meld($ X_{d a b d}$);
```

I get 0 for the first two and `X_{d a b d}`

for the last. Of course, they should all be nonzero. (For the last, if I then call canonicalise and meld again, I get 0 because it rearranges the indices into the first case.)

Similar behavior occurs with the simpler tensor

`X_{a b}_{c}::TableauSymmetry(shape=(2,1), indices=(0,2,1)).`

where

```
meld($ X_{a d d}$);
meld($ X_{d a d}$);
```

gives 0 for the first but `X_{d a d}`

for the second.

Perhaps I am doing something stupid but I don't quite see what it is.