For a paper I'm writing, I need a bit of second order logic in order to convey a few steps in an inference.
I've completed the introductory and intermediate/advanced logic classes at my school (second order logic wasn't included in the curriculum, unfortunately). I use predicate logic in most of my classes, so I'm comfortable with it.
I'd like to learn just enough to properly notate the steps of the inference.
Is there a concise tutorial on the subject available online?
There are not a lot of formal treatments of second-order logic that will include things like annotated formal deductions. I generally view Shapiro's book Foundations without foundationalism as the most contemporary treatment of second-order logic specifically - but it is written at a higher level, and will not discuss formal proofs much.
Some general-purpose logic texts may include second-order logic in particular chapters - the fourth edition of Mendelson's book does.