Start with some files

src/main/scala/leon/synthesis/Problem.scala

+package leon
+package synthesis
+
+case class Problem();

src/main/scala/leon/synthesis/Rules.scala

+package leon
+package synthesis
+
+/** AST definitions for Pure Scala. */
+object Rules {
+
+  abstract class Rule {
+    def isApplicable(p: Problem): Option[Step];
+  }
+
+}

src/main/scala/leon/synthesis/Solution.scala

+package leon
+package synthesis
+
+case class Solution();

src/main/scala/leon/synthesis/Step.scala

+package leon
+package synthesis
+
+case class Step(subProblems: List[Problem], construct: List[Solution] => Solution, score: Score);

src/main/scala/leon/synthesis/package.scala

+package leon
+
+package object synthesis {
+  type Score = Int
+
+}