diff -r 955d5b3b0619 -r 2849c305b12d progs/app61.scala
--- a/progs/app61.scala	Sun Oct 15 20:47:14 2017 +0100
+++ b/progs/app61.scala	Tue Oct 17 13:49:45 2017 +0100
@@ -6,12 +6,12 @@
   case Left(v) => Left(f1(v))
 }
 def F_SEQ(f1: Val => Val, f2: Val => Val) = (v:Val) => v match {
-  case Seq(v1, v2) => Seq(f1(v1), f2(v2))
+  case Sequ(v1, v2) => Sequ(f1(v1), f2(v2))
 }
 def F_SEQ_Empty1(f1: Val => Val, f2: Val => Val) = 
-  (v:Val) => Seq(f1(Empty), f2(v))
+  (v:Val) => Sequ(f1(Empty), f2(v))
 def F_SEQ_Empty2(f1: Val => Val, f2: Val => Val) = 
-  (v:Val) => Seq(f1(v), f2(Empty))
+  (v:Val) => Sequ(f1(v), f2(Empty))
 def F_ERROR(v: Val): Val = throw new Exception("error")
 
 // simplification of regular expressions returning also a