As with the case with Duke University's calendar, it is also common for there to be two months that differ due to the short number of days. In the case of Duke, June and July are slightly adjusted so the fiscal year can always begin on July 1 and end on June 30.
Let's review. A postulate is a statement accepted to be true without proof. Some common algebraic properties are also postulates and deal with the four operations: addition, subtraction, multiplication, and division. Other true statements are geometric postulates and include the ruler, angle addition, and segment addition postulates.
The term  axiom may also be used to refer to a background assumption. Example of a postulate: Through any two points in a plane there is exactly one straight line. A theorem is a statement that can be proven to be true based upon postulates and previously proven theorems.