Category Theory
Categories are difficult for computers to instantly describe its structure composed of various dimensions of arrows. Indeed there are many examples with much eraborations, using tools such as tikz/Tex or etc.
I would like to choose the way with hand-writing categories.
So it sometimes does not seem formal, but I will do my best.
The more urgent thing is, currently I think as a carpenter/architect, to get familiar with categories, which will be achieved with pencil and papers or degital alternatives like apple pencils.
Category theory is, needless to say, always studied or learned through nLab.
Under Construction.