 Throughout the videos, you may have noticed me reading code like this as x becomes the list 3, 7, 2, 5, and y becomes x sub 0. What's that sub all about? In algebra, when mathematicians want to represent a group of related variables, they write it like this, using a subscript for the index number. When computers first started being used for scientific purposes, programmers needed to represent lists, but they couldn't do subscripts on a teletype or punched cards. If they wrote something like this and read it as x0, x1, and x2, that wouldn't work because those are the names of independent variables, not part of a list. Those early programmers came up with a solution. They put the index number in square brackets to represent the subscript. In fact, in a language called FORTRAN, one name for a list was subscripted arrays. That's why we use brackets for indexes, and why we read them as x sub 0, x sub 1, x sub 2, etc. And that's the story of SUB.