Sam Isaacson

Closing as merged into https://github.com/SciML/Catalyst.jl/issues/515 to have one issue that tracks tutorials.

@ChrisRackauckas pointed out delays (constant only?) are supported via the `System` type. That being the case we should consider adding a conversion to that type, and a corresponding `DDEProblem` support.

Last I checked, on some platforms the Graphviz artifact is fine but on others it still has issues (i.e. last time I looked it wasn't working via artifacts on macs)....

I think it is still worth keeping this open, this would more be about testing the docstrings, which I don't think we can really do at the moment the way...

`System` seems to just accept `X(t-\tau)` directly, so maybe we can just let people type that (and add a check to see if there are delayed variables / capture them).

Is it just constant lags currently?

How could it be multiplication? That isn't valid in Julia is it?

I think this was settled, but @yewalenikhil65 feel free to reopen if there is something actionable in Catalyst still to do.

I like that. Clever!

The ModelingToolkit interface should just work: https://docs.sciml.ai/ModelingToolkit/stable/basics/Validation/ however, we need the `@variables` macro in the DSL so `t` can be specified with units by a user. Otherwise an incompatible units...