[task 2]: Use boolean judgments in rules 

https://github.com/LorenzoBettini/xsemantics/issues/issue/2

Change-Id: Ib6b238b01053584a7bc3560770b2d5793d374bc4
[task 5]: Add more judgment symbols (for upper and lower bound)

https://github.com/LorenzoBettini/xsemantics/issues/issue/5

Change-Id: Ibd73b4ab9156ab74b3d5d737d12981981a9e9077