Merge pull request #7 from SimonGuilloud/main

src/main/scala/lisa/kernel/fol/FormulaDefinitions.scala

src/main/scala/lisa/kernel/fol/TermDefinitions.scala

src/main/scala/lisa/kernel/proof/Judgement.scala

src/main/scala/lisa/kernel/proof/RunningTheory.scala

src/main/scala/lisa/settheory/SetTheoryDefinitions.scala

src/main/scala/lisa/settheory/SetTheoryTGAxioms.scala

src/main/scala/lisa/settheory/SetTheoryZAxioms.scala

src/main/scala/lisa/settheory/SetTheoryZFAxioms.scala

src/main/scala/proven/DSetTheory/Part1.scala

src/main/scala/proven/ElementsOfSetTheory.scala

src/test/scala/lisa/proven/SimpleProverTests.scala