protocol  prooftree     Proof General                    

4	  0.14 -         4.5 -

3         0.11 - 0.13    4.3pre130327 - 4.4
	              
2         0.9 - 0.10     4.2; 4.2pre120110 - 4.3pre130111               
	              
1         0.8            4.2pre120104                    