There are still some bugs left. I applied the meld function to my expression and it clearly changed.

I unloaded it before and after using the meld function, and the expressions were not equal, this can be seen at least by the fourth term in the upper expression and the last term in the lower expression.

Below is the code with the upper and lower expression and their comparison:

```
{a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,q,r,s,u,v,w,x,y,z#}::Indices(full,values={t,x,y}, position=independent).
\partial{#}::PartialDerivative.
\nabla{#}::Derivative.
{\nabla{#},\partial{#}}::Commuting.
h_{m? n?}::Metric.
h^{m? n?}::InverseMetric.
h_{m? n?}::Symmetric.
h^{m? n?}::Symmetric.
F_{m? n?}::AntiSymmetric.
\Gamma^{m}_{n q}::TableauSymmetry(shape={2}, indices={1,2}).
p::LaTeXForm("\pi").
G4p::LaTeXForm("G_{4\pi}").
G4X::LaTeXForm("G_{4X}").
G4XX::LaTeXForm("G_{4XX}").
G4Xp::LaTeXForm("G_{4\pi X}").
pi2::LaTeXForm("\pi^{m n}\pi_{m n}").
boxpi4::LaTeXForm("\Box^{(4)}{\pi}").
delboxpi4::LaTeXForm("\delta\Box^{(4)}{\pi}").
pi24::LaTeXForm("\pi^{\mu \nu}\pi_{\mu \nu}").
mathcalG:= G4 R_{a b}-2G4 \nabla_{a}(\phi) \nabla_{b}(\phi) (\phi)**(-1)-\nabla_{a}(\nabla_{b}(G4)) + \nabla_{c}(\nabla_{d}(G4)) h^{c d} h_{a b} - 1/2 F_{a c} F_{b d} G4 (\phi)**2 h^{c d}-2\nabla_{a}(G4X \nabla_{b}(p) boxpi4) + \nabla_{c}(G4X \nabla_{d}(p) boxpi4) h_{a b} h^{c d} + \nabla_{c}(G4X \nabla_{d}(\nabla_{a}(p)) \nabla_{b}(p)) h^{c d} + \nabla_{c}(G4X \nabla_{a}(\nabla_{d}(p)) \nabla_{b}(p)) h^{c d}-\nabla_{c}(G4X \nabla_{a}(\nabla_{b}(p)) \nabla_{d}(p)) h^{c d} + G4X ( - 1/2 (boxpi4)**2 h_{a b} + 1/2 h_{a b} pi24-2\nabla_{a}(\nabla_{c}(p)) \nabla_{b}(\nabla_{d}(p)) h^{c d} - 1/2 F_{a c} F_{b d} \nabla_{e}(p) \nabla_{f}(p) (\phi)**2 h^{c e} h^{d f}-2\nabla_{a}(\phi) \nabla_{c}(\phi) \nabla_{b}(p) \nabla_{d}(p) (\phi)**(-2) h^{c d} + F_{a c} F_{d e} \nabla_{b}(p) \nabla_{f}(p) (\phi)**2 h^{c d} h^{e f}) + G4XX ( - 1/2 \nabla_{a}(p) \nabla_{b}(p) (boxpi4)**2 + 1/2 \nabla_{a}(p) \nabla_{b}(p) pi24) + G4X boxpi4 (2\nabla_{a}(\nabla_{b}(p)) + 2\nabla_{a}(\phi) \nabla_{b}(p) (\phi)**(-1)) + R ( - 1/2 G4 h_{a b} - 1/2 G4X \nabla_{a}(p) \nabla_{b}(p));
mathcalG2 := G4 R_{a b}-2G4 \nabla_{a}(\phi) \nabla_{b}(\phi) (\phi)**(-1)-\nabla_{a}(\nabla_{b}(G4)) - 1/2 F_{a c} F_{b d} G4 (\phi)**2 h^{c d}-2\nabla_{a}(G4X \nabla_{b}(p) boxpi4) + \nabla_{c}(G4X \nabla_{d}(\nabla_{a}(p)) \nabla_{b}(p)) h^{c d} + G4X (-2\nabla_{a}(\nabla_{c}(p)) \nabla_{b}(\nabla_{d}(p)) h^{c d} - 1/2 F_{a c} F_{b d} \nabla_{e}(p) \nabla_{f}(p) (\phi)**2 h^{c e} h^{d f}-2\nabla_{a}(\phi) \nabla_{c}(\phi) \nabla_{b}(p) \nabla_{d}(p) (\phi)**(-2) h^{c d} + F_{a c} F_{d e} \nabla_{b}(p) \nabla_{f}(p) (\phi)**2 h^{c d} h^{e f} + ( - 1/2 (boxpi4)**2 + 1/2 pi24) h_{a b}) + G4XX ( - 1/2 (boxpi4)**2 + 1/2 pi24) \nabla_{a}(p) \nabla_{b}(p) + G4X boxpi4 (2\nabla_{a}(\nabla_{b}(p)) + 2\nabla_{a}(\phi) \nabla_{b}(p) (\phi)**(-1)) + R ( - 1/2 G4 h_{a b} - 1/2 G4X \nabla_{a}(p) \nabla_{b}(p)) + 2\nabla_{c}(\nabla_{d}(G4)) h^{c d} h_{a b};
test := @[mathcalG] - @[mathcalG2];
distribute(test);
canonicalise(test);
rename_dummies(test);
sort_product(test);
```