Merge pull request #6 from SimonGuilloud/main

src/main/scala/lisa/KernelHelpers.scala

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

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

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

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

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

src/main/scala/lisa/settheory/SetTheoryDefinitions.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/main/scala/proven/tactics/Destructors.scala

src/main/scala/proven/tactics/ProofTactics.scala