As a tribute to this bit of nostalgia, here's a wallpaper explaining one of the earliest facts one encounters in discrete mathematics, namely that the total number of subsets of an $n$-element set is $2^n$. There are any number of ways of proving this, and I have attempted to capture the one by induction --- in particular, the one where we observe that the new element either belongs, or does not belong, to one of the old subsets (that are made available inductively).