diff --git a/Include/bitset.h b/Include/bitset.h
new file mode 100644
index 0000000..63d69b4
--- /dev/null
+++ b/Include/bitset.h
@@ -0,0 +1,22 @@
+/* Bitset interface */
+
+#define BYTE		char
+
+typedef BYTE *bitset;
+
+bitset newbitset PROTO((int nbits));
+void delbitset PROTO((bitset bs));
+/* int testbit PROTO((bitset bs, int ibit)); /* Now a macro, see below */
+int addbit PROTO((bitset bs, int ibit)); /* Returns 0 if already set */
+int samebitset PROTO((bitset bs1, bitset bs2, int nbits));
+void mergebitset PROTO((bitset bs1, bitset bs2, int nbits));
+
+#define BITSPERBYTE	(8*sizeof(BYTE))
+#define NBYTES(nbits)	(((nbits) + BITSPERBYTE - 1) / BITSPERBYTE)
+
+#define BIT2BYTE(ibit)	((ibit) / BITSPERBYTE)
+#define BIT2SHIFT(ibit)	((ibit) % BITSPERBYTE)
+#define BIT2MASK(ibit)	(1 << BIT2SHIFT(ibit))
+#define BYTE2BIT(ibyte)	((ibyte) * BITSPERBYTE)
+
+#define testbit(ss, ibit) (((ss)[BIT2BYTE(ibit)] & BIT2MASK(ibit)) != 0)