Write once, run everywhere

==========================

  	Good idea, but still wishful thinking.

	From my experience I would like to add:

        "Write once, run everywhere, show the same behaviour!"	

Known bugs and failures:

========================

- Cut-and-paste

	I have not included any code for cut-and-paste. However,

	cut-and-paste should work fine under Unix. Cut-and-Paste

	also works in MS IE 3.0 under Mickeysoft Windows. For most of 

        the other platforms (MacOS etc.) and browsers (Netscape etc.)

        cut-and-paste does not work.

- Security exception

	Various versions of Netscape throw a security exception when

	I try to suspend the thread of the proof search. I have caught 

	this exception, but my literature does not tell me how to resume 

	safely from this exception. In effect the proof search enumerates 

 	all possible proofs for a sequent and subsequently stops. The user 

	has no control over how many proofs are shown (the corresponding 

	windows might appear over each other). This unintended behaviour 

	has been encountered in:

	  - Netscape Navigator 3.0 Gold under MS Windows'45

	  - Netscape Navigator 3.0 under MacOS

          - Netscape Communicator 4.0 under MacOS

	  - Netscape Navigator 3.01 Gold under Linux

	      (But here a "catch" of this exception and a "do nothing" 

	       helps. God knows why.)

	  - possible others

- Boxes around the sequents in proofs

	I have modified the "Label" class such that the "MyLabel" class 

	has a surrounding box. This improves the readability of the proofs.

	However,  this feature works ONLY under Unix. The boxes do not 

	appear in MS Windows and MacOS (reason unknown). 

- Flickering messages

	The applet prints some messages ("Grammar error", "No more proofs",

	"Not provable", etc.) in a field below the control buttons. 

	In some browsers the messages only flicker for a short time.

	Other browsers show the messages correctly (reason unknown).

The applet has been tested under (but see restrictions and bugs):

=================================================================

Linux:   

        Netscape Navigator 3.01 Gold

	Netscape Communicator 4.03, 4.04, 4.07 

        HotJava 1.1 beta2 (Linux-port)

        SUN's appletviewer for JDK 1.1.3

Win'95:

        Netscape Navigator 3.0 Gold

	Netscape Communicator 4.01a

        MS Internet Explorer 3.0.2

	MS Internet Explorer 4.0	

MacOS:  

	Netscape Navigator 3.0

	Netscape Communicator 4.0

	MS Internet Explorer 3.0.1b1 (PowerPC)

Any comments on success or failure for other

environments and platforms are appreciated.  

Christian.Urban@cl.cam.ac.uk