I started to study economics. Since I majored in Mathematics, I'd like to learn the principles of macroeconomics through the analysis of a simple economic models (using equations). That's why I looking for a book that teaches some simple economic models.
My question is: which book teaches about a simple economic model that presents concepts like GDP, aggregate demand and supply curves, inflationary gap, demand-pull inflation, diminishing returns, etc?
The materials that I found don't explain very well some equations. For instance, they usually use the variable $Y$ for aggregate output, but also uses variations $Y_a$, $Y_d$, $Y_p$ to denote disposable person income, disposable income, and potential GDP, respectively, without explaining the difference between those concepts.
Thank you for your attention!