diff -r 6e2cef17a9b3 -r 6756b026c5fe exps/both.scala
--- a/exps/both.scala	Thu Feb 07 10:52:41 2019 +0000
+++ b/exps/both.scala	Fri Feb 08 12:47:35 2019 +0000
@@ -114,7 +114,7 @@
 }
  
 
-//--------------------------------------------------------------------------------------------------------
+//--------------------------------------------------------------
 // START OF NON-BITCODE PART
 //
 
@@ -264,12 +264,43 @@
 
 def lexing_simp(r: Rexp, s: String) : Val = lex_simp(r, s.toList)
 
-println(lexing_simp(("a" | "ab") ~ ("b" | ""), "ab"))
+//println(lexing_simp(("a" | "ab") ~ ("b" | ""), "ab"))
+
+
+def tokenise_simp(r: Rexp, s: String) = 
+  env(lexing_simp(r, s)).map(esc2)
+
+//--------------------------------------------------------------------
+// Partial Derivatives
 
 
-def tokenise_simp(r: Rexp, s: String) = env(lexing_simp(r, s)).map(esc2)
+def pder(c: Char, r: Rexp): Set[Rexp] = r match {
+  case ZERO => Set()
+  case ONE => Set()
+  case PRED(f, _) => if (f(c)) Set(ONE) else Set()
+  case ALTS(rs) => rs.toSet.flatMap(pder(c, _))
+  case SEQ(r1, r2) =>
+    (for (pr1 <- pder(c, r1)) yield SEQ(pr1, r2)) ++
+    (if (nullable(r1)) pder(c, r2) else Set())
+  case STAR(r1) =>
+    for (pr1 <- pder(c, r1)) yield SEQ(pr1, STAR(r1))
+  case RECD(_, r1) => pder(c, r1)
+}
 
-//--------------------------------------------------------------------------------------------------------
+def pders(cs: List[Char], r: Rexp): Set[Rexp] = cs match {
+  case Nil => Set(r)
+  case c::cs => pder(c, r).flatMap(pders(cs, _))
+}
+
+def pders_simp(cs: List[Char], r: Rexp): Set[Rexp] = cs match {
+  case Nil => Set(r)
+  case c::cs => pder(c, r).flatMap(pders_simp(cs, _)).map(simp(_)._1)
+}
+
+def psize(rs: Set[Rexp])  = 
+  rs.map(size).sum
+
+//--------------------------------------------------------------------
 // BITCODED PART
 
 
@@ -595,7 +626,7 @@
 println("Size Bit  " + asize(bders_simp((fib_prog * 1).toList, internalise(WHILE_REGS))))
 println("Size Bitf " + asize(bders_simp_full((fib_prog * 1).toList, internalise(WHILE_REGS))))
 println("Size Old  " + size(ders_simp((fib_prog * 1).toList, WHILE_REGS)))
-
+println("Size Pder " + psize(pders_simp((fib_prog * 1).toList, WHILE_REGS)))
 
 System.exit(0)