start to work on set theory thorems

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

+package proven.DSetTheory
+import lisa.kernel.fol.FOL.*
+import lisa.kernel.proof.SequentCalculus.*
+import lisa.KernelHelpers.{*, given}
+import lisa.kernel.Printer
+import proven.tactics.ProofTactics.*
+import proven.tactics.Destructors.*
+import lisa.settheory.AxiomaticSetTheory.*
+
+import scala.collection.immutable.SortedSet
+import lisa.kernel.proof.{SCProof, SCProofChecker}
+
+import scala.collection.immutable
+object Part1 {
+
+/**
+
+ */
+val noSetCOntainsItself: SCProof = {
+    val contra = (y in y) <=> !(y in y)
+    val s1 = Hypothesis(contra |- contra, contra)
+    val s2 = LeftForall
+
+}
+}