diff -r b47e140bcccd -r 47a299e7010f progs/re3.scala
--- a/progs/re3.scala	Thu Jul 25 14:39:37 2019 +0100
+++ b/progs/re3.scala	Sun Jul 28 01:00:41 2019 +0100
@@ -14,7 +14,7 @@
 
 
 
-// nullable function: tests whether the regular 
+// the nullable function: tests whether the regular 
 // expression can recognise the empty string
 def nullable (r: Rexp) : Boolean = r match {
   case ZERO => false
@@ -26,7 +26,7 @@
   case NTIMES(r, i) => if (i == 0) true else nullable(r)
 }
 
-// derivative of a regular expression w.r.t. a character
+// the derivative of a regular expression w.r.t. a character
 def der (c: Char, r: Rexp) : Rexp = r match {
   case ZERO => ZERO
   case ONE => ZERO
@@ -57,35 +57,35 @@
 }
 
 
-// derivative w.r.t. a string (iterates der)
+// the derivative w.r.t. a string (iterates der)
 def ders(s: List[Char], r: Rexp) : Rexp = s match {
   case Nil => r
   case c::s => ders(s, simp(der(c, r)))
 }
 
-// derivative w.r.t. a string (iterates der)
+// the derivative w.r.t. a string (iterates der)
 def dersp(s: List[Char], r: Rexp) : Rexp = s match {
   case Nil => r
   case c::s => dersp(s, der(c, r))
 }
 
 
-// main matcher function
+// the main matcher function
 def matcher(r: Rexp, s: String) : Boolean = nullable(ders(s.toList, r))
 
-//tests
+// tests
 val q = SEQ(SEQ(CHAR('x'), CHAR('y')), CHAR('z'))
 dersp("x".toList, q)
 dersp("xy".toList, q)
 dersp("xyz".toList, q)
 
-//one or zero
+// one or zero
 def OPT(r: Rexp) = ALT(r, ONE)
 
 
 // Test Cases
 
-//evil regular expressions: (a?){n} a{n}  and (a*)* b
+// evil regular expressions: (a?){n} a{n}  and (a*)* b
 def EVIL1(n: Int) = SEQ(NTIMES(OPT(CHAR('a')), n), NTIMES(CHAR('a'), n))
 val EVIL2 = SEQ(STAR(STAR(CHAR('a'))), CHAR('b'))