diff --git a/kern/include/lib.h b/kern/include/lib.h
index 7478ce6..b010a7b 100644
--- a/kern/include/lib.h
+++ b/kern/include/lib.h
@@ -194,5 +194,7 @@ void kprintf_bootstrap(void);
 #define DIVROUNDUP(a,b) (((a)+(b)-1)/(b))
 #define ROUNDUP(a,b)    (DIVROUNDUP(a,b)*b)
 
+void random_yielder(uint32_t);
+void random_spinner(uint32_t);
 
 #endif /* _LIB_H_ */
diff --git a/kern/include/overwrite.h b/kern/include/overwrite.h
index 4a3b220..cf58fce 100644
--- a/kern/include/overwrite.h
+++ b/kern/include/overwrite.h
@@ -40,6 +40,6 @@
  * testing.
  */
 
-#define KERNEL_PROMPT    "OS/161 kernel [? for menu]: "
+#define KERNEL_PROMPT "OS/161 kernel [? for menu]: "
 
 #endif /* _OVERWRITE_H_ */
diff --git a/kern/lib/misc.c b/kern/lib/misc.c
index 2388e1d..c22d88c 100644
--- a/kern/lib/misc.c
+++ b/kern/lib/misc.c
@@ -30,6 +30,7 @@
 #include <types.h>
 #include <kern/errmsg.h>
 #include <lib.h>
+#include <thread.h>
 
 /*
  * Like strdup, but calls kmalloc.
@@ -60,3 +61,27 @@ strerror(int errcode)
 	panic("Invalid error code %d\n", errcode);
 	return NULL;
 }
+
+/*
+ * Helper functions used by testing and problem driver code
+ * to establish better mixtures of threads.
+ */
+
+void
+random_yielder(uint32_t max_yield_count)
+{
+	uint32_t i;
+	for (i = 0; i < random() % max_yield_count; i++) {
+		thread_yield();
+	}
+}
+
+void
+random_spinner(uint32_t max_spin_count)
+{
+	uint32_t i;
+	volatile int spin;
+	for (i = 0; i < random() % max_spin_count; i++) {
+		spin += i;
+	}
+}