In the example [Mean-field Two-sided Cavity](https://qojulia.github.io/QuantumInputOutput.jl/dev/examples/04-2_two-sided-cavity_with-atom_coh-drive__cumulants/#Mean-field-Two-sided-Cavity), we should replace `t = meanfield([a], -Δ*a'a, [a]).iv` by `@independent_variables t`.
In the example Mean-field Two-sided Cavity, we should replace
t = meanfield([a], -Δ*a'a, [a]).ivby@independent_variables t.