Jason Zimba is working on a technical manual that will describe higher order structures in the Common Core standards, such as flows, streams, and ties. Here is an example of what is meant by a flow. What I like about this diagram is that it illustrates the way mathematical ideas are unified as the subject progresses. For example, the disparate ideas of whole number, fraction, decimal, integer, and rational number are unified in an understanding of the number system. Mathematics doesn’t branch out and get more complicated, it collates and compacts ideas into more powerful and denser ideas.