אo - Aleph naught - The first letter of the Hebrew alphabet, א is used to represent the countable infinity. Imagine that you start counting
1,2,3,... , when would you stop? Well, never, but we do know how many
counting numbers there are... אo.
δ - delta - This greek letter has many uses in modern mathematics. It is most commonly used to represent the smallest positive number when observing an infinitesimal change. A use more relevant to the newlyweds is the distinction of the degree of a vertex in a graph.
From the Back