Continued fractions           Cf
   pr =. +%

   4 pr 5
4.2

   5 pr 4
5.25
   1 pr 1
2
   1 pr 1 pr 1
1.5
   1 pr ( 1 pr 1)
1.5
   ( 1 pr 1 ) pr 1
3
   pr / 1 1 1
1.5
   ] a =. 10 $  1
1 1 1 1 1 1 1 1 1 1
   pr / \ 10 $ a
1 2 1.5 1.66667 1.6 1.625 1.61538 1.61905 1.61765 1.61818
