In mathematics, infinity is the conceptual expression of such a numberless number. It is often symbolized by the lemniscate (also known as the lemniscate of Bernoulli), which looks something like the numeral 8 written sideways (). This symbol for infinity was first used in the 1600s by the mathematician John Wallis.
An epic is a poem; most epics started as oral tales that were passed down from generation to generation (often in the form of songs), which is why they're poems. A legend and a myth are more similar, but a myth most often explains something about the universe. So while there might be a legend about a man who slayed all the dragons, a myth would be about the man who caused it to rain, or how humans were created. Those are the basics differences.
Ideas are forever. There are many important differences between Greek tragedy and Shakespearean tragedy. Greek tragedy was performed as part of a religious festival (like a church christmas play) - so the stories were already known to the audience, and everyone knew what was going to happen next.