diff -r 2969ee4a6cee -r ca9c1cf929fa progs/sudoku.scala
--- a/progs/sudoku.scala	Fri Nov 22 17:01:55 2019 +0000
+++ b/progs/sudoku.scala	Tue Nov 26 01:22:36 2019 +0000
@@ -53,6 +53,17 @@
       map(c => search(update(game, empty(game), c))).toList.flatten
 }
 
+def search1T(games: List[String]): Option[String] = games match {
+  case Nil => None
+  case game::rest => {
+    if (isDone(game)) Some(game)
+    else {
+      val cs = candidates(game, emptyPosition(game))
+      search1T(cs.map(c => update(game, empty(game), c)) ::: rest)
+    }
+  }
+}
+
 // a list of hard games according to Andrew Coles and Peter Norvig
 
 val hard_games =