try to fit any knot into any one of six different sized tubes
using the 1x2, 1x3, 1x4, 2x2, 2x3 and 3x3 commands

example usage:
1x2 7_6
1x3 4_1
2x2 6_3
2x3 8_7
1x4 8_3
2x2 8_17
2x2 9.3
3x3 10.66
2x2 10.123
2x2 8.2.6

entire Rolfsen Appendix C is available
use _ for proper knots less than nine crossings

note: the 1x2, 1x3, 1x4, 2x2, 2x3 and 3x3 commands are defined for this KnotPlot session
(i.e., you don't have to click the `PxQ-tube' button again)
