Hello,

I've found situations where `meld`

returns an incorrect 0, when applied on some undistributed sums, namely

```
(w_{a} x_{b} y_{c}-w_{c} x_{b} y_{a}) f^{a c}
(w_{a} x_{b} y_{c} z_{d}-w_{c} x_{b} y_{a} z_{d}) f^{a b c}
(w_{a} x_{b} y_{c} z_{d}-w_{c} x_{b} y_{a} z_{d}) f^{a b c d}
```

More precisely, the above 3 lines are the output corresponding to the following input:

```
{a,b,c,d,e#}::Indices(Lorentz,parent=ambient).
f^{a b}::TableauSymmetry(shape=(1,1),indices=(0,1)).
f^{a b c}::TableauSymmetry(shape=(2,1),indices=(0,1,2)).
f^{a b c d}::TableauSymmetry(shape=(2,2),indices=(0,1,2,3)).
fac:=f^{a c}.
fabc:=f^{a b c}.
fabcd:=f^{a b c d};
Dwy:=(w_{a} y_{c} - w_{c} y_{a}).
Dwxy:=(w_{a} x_{b} y_{c} - w_{c} x_{b} y_{a}).
Dwyz:=(w_{a} y_{c} z_{d} - w_{c} y_{a} z_{d}).
Dwxyz:=(w_{a} x_{b} y_{c} z_{d} - w_{c} x_{b} y_{a} z_{d}).
for f in [fac,fabc,fabcd]:
for D in [Dwy,Dwxy,Dwyz,Dwxyz]:
fD=f*D
meld(fD)
if fD==0:
print(f*D)
Df=D*f
meld(Df)
if Df==0:
print(D*f)
```