For example:

```
{t,z,x,y,w}::Coordinate.
{\mu,\nu,\rho,\sigma,\alpha,\beta,\gamma,\lambda,\tau,\pi,\xi,\iota,\omega,\kappa,\psi,\epsilon,\upsilon,p}::Indices(values={t,z,x,y,w},position=independent).
g_{\mu\nu}::Metric.
g^{\mu\nu}::InverseMetric.
metric:=[g_{t t}=-E**{2A} g z**{-2},g_{z z}=E**{2A} g**{-1} z**{-2},g_{x x}=E**{2A+\chi} z**{-2},g_{y y}=E**{2A} z**{-2},g_{w w}=E**{2A} z**{-2}];
complete(_,$g^{\mu\nu}$);
F:={F_{t t}=0,F_{t z}=-\partial_{z}{A_{t}},F_{t x}=0,F_{t y}=0,F_{t w}=0,
F_{z t}=\partial_{z}{A_{t}},F_{z z}=0,F_{z x}=0,F_{z y}=0,F_{z w}=0,
F_{x t}=0,F_{x z}=0,F_{x x}=0,F_{x y}=0,F_{x w}=0,
F_{y t}=0,F_{y z}=0,F_{y x}=0,F_{y y}=0,F_{y w}=B,
F_{w t}=0,F_{w z}=0,F_{w x}=0,F_{w y}=-B,F_{w w}=0 };
ex:=g^{\mu\nu} F_{\mu\nu};
evaluate(_,metric+F, rhsonly=True);
```

The error message is

```
RuntimeError: substitute: Argument is neither a replacement rule nor an equality
At:
Notebook Cell (Line 15): _ = evaluate(_,metric+F, rhsonly=True); display(_)
```

What's wrong ? This was not an issue in the older versions.