http://thesis.vt.edu 50 virginia tech thesis
   http://thesis.vt.edu/thesis1.html 20 graph theory longword
      http://thesis.vt.edu/thesis1/ch1 10 vertex-edge
      http://thesis.vt.edu/thesis1/ch2 10 graph theoery
         http://thesis.vt.edu/thesis1/ch2/seca 2 directed cycled graph
         http://thesis.vt.edu/thesis1/ch2/secb 3 directed acycled graph
         http://thesis.vt.edu/thesis1/ch2/secc 4 tree structure
   http://thesis.vt.edu/thesis2/ 3 regular expression
      http://thesis.vt.edu/thesis2/ch1 8 defination
         http://thesis.vt.edu/thesis2/ch2/seca 3 regular expression structure
         http://thesis.vt.edu/thesis2/ch2/secb 3 linux regular expression
         http://thesis.vt.edu/thesis2/ch2/secc 4 windows regular expression
   http://thesis.vt.edu/thesis3 5 approximation sorting
      http://thesis.vt.edu/thesis3/ch1 10 approximation
         http://thesis.vt.edu/thesis3/ch2 2 mathematical calculation