ZHANG, Ruda August 07, 2020:  Correct math: use 1 with set subscript for characteristic function / indicator function of the set; use "[ x ]" instead of "[x]" to avoid GFM checkbox syntax. [1ac98ba]
ZHANG, Ruda January 18, 2020:  Convert math-text words to text only when the math symbols are ASCII only. [e4c945c]
ZHANG, Ruda December 05, 2019:  More on manifolds, from John Marshall Lee's textbooks. [6ba9029]
ZHANG, Ruda August 08, 2019:  Formating; separate duality theorems; add Vehicle Routing Problem [fbfb8ee]