The generalization of this lemma permits opening of the angles beyond , as far reflex as they were originally convex. The conclusion remains the same: e cannot shorten.
This theorem can be derived from Chern's proof^{1} of a theorem of Axel Schur^{2}, employing differential geometry, or, independently, by induction [O'R00].
The turn angle ranges are displayed in green, and the "forbidden shoulder circle" is drawn in blue. The user may then turn any joint of the chain by doubleclicking on it and dragging the next link:
The theorem says that no reconfiguration within the allowable turn angle ranges will permit the hand to enter the forbidden circle:
A corollary says that every joint has a correspoding forbidden circle, which can be viewed by selecting:View all concentric circles
For more details, see the paper [O'R00] or view Help on applet.
Platform  OS  Browser  
Internet Explorer  Netscape Communicator  
PC  Windows 9x, WindowsNT4  IE v4: No reported problems on above resolution.  NC v4.7: No reported problems on above resolution. 
Red Hat Linux 6.1  Not tested.  Netscape v4.61 for Linux. No reported problems.  
MAC  MacOS 8.5  IE v4: No reported problems at above resolutions.  Some Mac versions of Netscape do not support the Java1.2 event model, which is used extensively on the applet. Therefore, IE is recommended for the Mac 
SGI  Irix 6.x  Not tested.  Tested on Netscape 4.07. Reported problems are:
