Ahhh, good point !! My bad!
Ahh, yes, that is correct. I am merely trying to build on the shoulders of titans 
This is where I have trouble understanding the issue. If Todo.System.start_link returns the type Supervisor.on_start, then your Todo.Application.start, which returns whatever Todo.System.start_link returns, should return the same.
The error should still be there, as Todo.System.start_link can in theory still return :ignore, thus causing the signature to be different. Am I miss interpreting something?
