diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..98e59e0
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,22 @@
+# .gitignore padrão Scala, SBT no VSCode com plugin Scala Metals
+*.class
+*.log
+.bloop/
+.metals/
+.vscode/
+.scalafmt.conf
+project/
+
+# virtual machine crash logs, see http://www.java.com/en/download/help/error_hotspot.xml
+hs_err_pid*
+
+# Simple Build Tool
+# http://www.scala-sbt.org/release/docs/Getting-Started/Directories.html#configuring-version-control
+
+dist/*
+target/
+lib_managed/
+src_managed/
+.history
+.cache
+.lib/
diff --git a/src/main/scala/br/unb/cic/wlang/AvailableExpression.scala b/src/main/scala/br/unb/cic/wlang/AvailableExpression.scala
new file mode 100644
index 0000000..45cfbae
--- /dev/null
+++ b/src/main/scala/br/unb/cic/wlang/AvailableExpression.scala
@@ -0,0 +1,56 @@
+package br.unb.cic.wlang
+import scala.collection.mutable
+
+/** Implementation of the Available Expression algorithm.
+  */
+
+object AvailableExpression {
+//   TODO getNonTrivialExpressionSet
+//   TODO setInitialValues = Emptyset
+//   TODO Naive Chaotic Iteration on AvailableExpression.execute
+  type Abstraction = Set[(String, Stmt)]
+  type DS = mutable.HashMap[Stmt, Abstraction]
+
+  val empty: Abstraction = Set.empty
+
+  def execute(program: WhileProgram): (DS, DS) = {
+    val cfg = CFGBuilder.build(program)
+    val stmts = CFGBuilder.stmts(program)
+
+    // initialization
+    val universalSet = initUniversalSet(program.stmt)
+    val out = initOutSet(stmts)
+    val in = new DS()
+
+    var fixedPoint = false
+
+    // while (!fixedPoint) {} //TODO
+    (in, out)       //é o return (DS, DS)
+  }
+
+  def initOutSet(stmts: Set[Stmt]): DS = { //inicializa os sets dos stmts como vazio? ok!
+    val out = new DS()
+    stmts.foreach(s => out += s -> empty)
+    out
+  }
+
+  def initUniversalSet(stmt: Stmt): Abstraction = stmt match {
+    case Assignment(v, _, _) => Set((v, stmt))
+    case Skip(_)             => Set.empty
+    case IfThenElse(_, s1, s2, _) =>
+      initUniversalSet(s1) union initUniversalSet(s2)
+    case While(_, s, _)   => initUniversalSet(s)
+    case Sequence(s1, s2) => initUniversalSet(s1) union initUniversalSet(s2)
+  }
+
+  def kill(stmt: Stmt, universalSet: Abstraction): Abstraction = stmt match {
+    case Assignment(v, _, _) => universalSet.filter(t => v == t._1)
+    case _                   => Set.empty
+  }
+
+  def gen(stmt: Stmt): Abstraction = stmt match {
+    case Assignment(v, _, _) => Set((v, stmt))
+    case _                   => Set.empty
+  }
+
+}
diff --git a/src/main/scala/br/unb/cic/wlang/ReachDefinition.scala b/src/main/scala/br/unb/cic/wlang/ReachDefinition.scala
index 282e52f..1e257af 100644
--- a/src/main/scala/br/unb/cic/wlang/ReachDefinition.scala
+++ b/src/main/scala/br/unb/cic/wlang/ReachDefinition.scala
@@ -27,25 +27,25 @@ object ReachDefinition {
     while(!fixedPoint) {
       val (oldIn, oldOut) = (in.clone(), out.clone())
       for(s <- stmts) {
-        //IN[S] = U {OUT[from] | (from, to) in cfg, S == to}
+        //IN[S] = U {OUT[from] | (from, to) in cfg, S == to}  //OK conforme definição do livro para o RDEntry(to)
         //This is not so beautiful in Scala =(
-        in(s) =  (for { (from,to) <- cfg if to == s } yield out(from)).foldLeft(empty)(_ union _)
+        in(s) =  (for { (from,to) <- cfg if to == s } yield out(from)).foldLeft(empty)(_ union _) //não consegui ler esse trecho
 
-        //OUT[S] = GEN(S) U (IN[S] - KILL[S])
-        out(s) = gen(s) union (in.getOrElse(s, empty) diff kill(s, universalSet))
+        //OUT[S] = GEN(S) U (IN[S] - KILL[S]) //OK conforme definição do livro para o RDexit(to)
+        out(s) = gen(s) union (in.getOrElse(s, empty) diff kill(s, universalSet)) //não consegui ler esse trecho
       }
-      fixedPoint = (oldIn, oldOut) == (in, out)
+      fixedPoint = (oldIn, oldOut) == (in, out) //Se não há mais alterações nos conjuntos entre RDentry(from), RDexit(from) e RDentry(to), RDexit(to) então chegou no fixed point e sai do laço
     }
     (in, out)
   }
 
-  def initOutSet(stmts: Set[Stmt]): DS = {
+  def initOutSet(stmts: Set[Stmt]): DS = { //inicializa os sets dos stmts como vazio? ok!
     val out = new DS()
     stmts.foreach(s => out += s -> empty)
     out
   }
 
-  def initUniversalSet(stmt: Stmt): Abstraction = stmt match  {
+  def initUniversalSet(stmt: Stmt): Abstraction = stmt match  { //não entendi a necessidade desse inituniversal
     case Assignment(v, _, _) => Set((v, stmt))
     case Skip(_) => Set.empty
     case IfThenElse(_, s1, s2, _) => initUniversalSet(s1) union initUniversalSet(s2)
@@ -54,12 +54,12 @@ object ReachDefinition {
   }
 
   def kill(stmt: Stmt, universalSet: Abstraction): Abstraction = stmt match {
-    case Assignment(v, _, _) => universalSet.filter(t => v == t._1)
+    case Assignment(v, _, _) => universalSet.filter(t => v == t._1) //filtra true/false mas não entendi como o 't._1' é true somente p/ assignments a 'v'
     case _ => Set.empty
   }
 
   def gen(stmt: Stmt): Abstraction = stmt match {
-    case Assignment(v, _, _) => Set((v,stmt))
+    case Assignment(v, _, _) => Set((v,stmt))  //v = nome da variável que está sendo definida no Assignment
     case _ => Set.empty
   }
 
diff --git a/src/test/scala/br/unb/cic/wlang/AvailableExpressionTest.scala b/src/test/scala/br/unb/cic/wlang/AvailableExpressionTest.scala
new file mode 100644
index 0000000..12bdd17
--- /dev/null
+++ b/src/test/scala/br/unb/cic/wlang/AvailableExpressionTest.scala
@@ -0,0 +1,22 @@
+package br.unb.cic.wlang
+
+import org.scalatest.funsuite.AnyFunSuite
+
+class AvailableExpressionTest extends AnyFunSuite {
+
+  /*
+ * x := a+b;
+ * y := a*b;
+ * while y > a+b do
+ *     a := a+l;
+ *     x := a+b;
+*/
+
+  val s1 = Assignment("x", Add(Var("a"), Var("b")), 1)
+  val s2 = Assignment("y", Mult(Var("a"), Var("b")), 2)
+  val s4 = Assignment("a", Add(Var("a"), Const(1)), 4)
+  val s5 = Assignment("x", Add(Var("a"), Var("b")), 5)
+  val s3 = While(GT(Var("y"), Add(Var("a"), Var("b"))), s2, 4)
+  val p = WhileProgram(Sequence(s1, Sequence(s2, Sequence(s3, Sequence(s4, s5)))))
+
+}