diff --git a/user/< b/user/<
deleted file mode 100644
index d51e048..0000000
--- a/user/<
+++ /dev/null
@@ -1,255 +0,0 @@
-// implement fork from user space
-
-#include "lib.h"
-#include <mmu.h>
-#include <env.h>
-
-
-/* ----------------- help functions ---------------- */
-
-/* Overview:
- * 	Copy `len` bytes from `src` to `dst`.
- *
- * Pre-Condition:
- * 	`src` and `dst` can't be NULL. Also, the `src` area 
- * 	 shouldn't overlap the `dest`, otherwise the behavior of this 
- * 	 function is undefined.
- */
-void user_bcopy(const void *src, void *dst, size_t len)
-{
-	void *max;
-
-	//	writef("~~~~~~~~~~~~~~~~ src:%x dst:%x len:%x\n",(int)src,(int)dst,len);
-	max = dst + len;
-
-	// copy machine words while possible
-	if (((int)src % 4 == 0) && ((int)dst % 4 == 0)) {
-		while (dst + 3 < max) {
-			*(int *)dst = *(int *)src;
-			dst += 4;
-			src += 4;
-		}
-	}
-
-	// finish remaining 0-3 bytes
-	while (dst < max) {
-		*(char *)dst = *(char *)src;
-		dst += 1;
-		src += 1;
-	}
-
-	//for(;;);
-}
-
-/* Overview:
- * 	Sets the first n bytes of the block of memory 
- * pointed by `v` to zero.
- * 
- * Pre-Condition:
- * 	`v` must be valid.
- *
- * Post-Condition:
- * 	the content of the space(from `v` to `v`+ n) 
- * will be set to zero.
- */
-void user_bzero(void *v, u_int n)
-{
-	char *p;
-	int m;
-
-	p = v;
-	m = n;
-
-	while (--m >= 0) {
-		*p++ = 0;
-	}
-}
-/*--------------------------------------------------------------*/
-
-/* Overview:
- * 	Custom page fault handler - if faulting page is copy-on-write,
- * map in our own private writable copy.
- * 
- * Pre-Condition:
- * 	`va` is the address which leads to a TLBS exception.
- *
- * Post-Condition:
- *  Launch a user_panic if `va` is not a copy-on-write page.
- * Otherwise, this handler should map a private writable copy of 
- * the faulting page at correct address.
- */
-static void
-pgfault(u_int va)
-{
-	u_int *tmp;
-	int ret;
-	//	writef("fork.c:pgfault():\t va:%x\n",va);
-    if ((((Pte *)(*vpt))[VPN(va)] & PTE_COW) == 0)
-	{
-		user_panic("User pgfault face a not COW page!");
-	}
-	va = ROUNDDOWN(va, BY2PG);
-	tmp = USTACKTOP; // have a page of invalid memory.
-    //map the new page at a temporary place
-	ret = syscall_mem_alloc(0, tmp, PTE_V | PTE_R);
-	if (ret < 0)
-	{
-		user_panic("User pgfault alloc faild!");
-	}
-
-	//copy the content
-	user_bcopy(va, tmp, BY2PG);
-    //map the page on the appropriate place
-	ret = syscall_mem_map(0, tmp, 0, va, PTE_V | PTE_R);
-	if (ret < 0)
-	{
-		user_panic("User pgfault map faild!");
-	}
-    //unmap the temporary place
-	ret = syscall_mem_unmap(0, tmp);
-	if (ret < 0)
-	{
-		user_panic("User pgfault umap faild!");
-	}
-	return;
-}
-
-/* Overview:
- * 	Map our virtual page `pn` (address pn*BY2PG) into the target `envid`
- * at the same virtual address. 
- *
- * Post-Condition:
- *  if the page is writable or copy-on-write, the new mapping must be 
- * created copy on write and then our mapping must be marked 
- * copy on write as well. In another word, both of the new mapping and
- * our mapping should be copy-on-write if the page is writable or 
- * copy-on-write.
- * 
- * Hint:
- * 	PTE_LIBRARY indicates that the page is shared between processes.
- * A page with PTE_LIBRARY may have PTE_R at the same time. You
- * should process it correctly.
- */
-static void
-duppage(u_int envid, u_int pn)
-{
-	u_int addr;
-	u_int perm;
-	writef("%x\n",((Pte *)(*vpt))[pn]);
-	addr = pn << PGSHIFT;
-	perm = ((Pte *)(*vpt))[pn] & 0xfff;
-	if (addr == UTOP - 2 * BY2PG)
-	{
-		writef("here\n");
-	}
-	if ((perm & PTE_R) == 0)
-	{
-		if(syscall_mem_map(0, addr, envid, addr, perm) < 0)
-		{
-			user_panic("user panic mem map error!1");
-		}
-	}
-	else if (perm & PTE_LIBRARY)
-	{
-		if(syscall_mem_map(0, addr, envid, addr, perm) < 0)
-		{
-			user_panic("user panic mem map error!2");
-		}
-	}
-	else if (perm & PTE_COW)
-	{
-		if(syscall_mem_map(0, addr, envid, addr, perm) < 0)
-		{
-			user_panic("user panic mem map error!3");
-		}
-	}
-	else
-	{	
-		if(syscall_mem_map(0, addr, envid, addr, perm | PTE_COW) < 0)
-		{
-			user_panic("user panic mem map error!4");
-		}
-		if(syscall_mem_map(0, addr, 0, addr, perm | PTE_COW) < 0)
-		{
-			user_panic("user panic mem map error!5");
-		}
-	}
-
-	//	user_panic("duppage not implemented");
-}
-
-/* Overview:
- * 	User-level fork. Create a child and then copy our address space
- * and page fault handler setup to the child.
- *
- * Hint: use vpd, vpt, and duppage.
- * Hint: remember to fix "env" in the child process!
- * Note: `set_pgfault_handler`(user/pgfault.c) is different from 
- *       `syscall_set_pgfault_handler`. 
- */
-extern void __asm_pgfault_handler(void);
-int
-fork(void)
-{
-	// Your code here.
-	u_int newenvid;
-	extern struct Env *envs;
-	extern struct Env *env;
-	u_int i;
-	int ret;
-
-
-	//The parent installs pgfault using set_pgfault_handler
-	set_pgfault_handler(pgfault);
-	//alloc a new alloc
-
-	newenvid = syscall_env_alloc();
-	if (newenvid == 0)
-	{
-		env = envs + ENVX(syscall_getenvid());
-		return 0;
-	}
-	//writef("%x",newenvid);
-
-	//writef("begin\n");
-
-	for (i = 0; i < UTOP -  1 * BY2PG; i += BY2PG)
-	{
-		if ((((Pde *)(*vpd))[i >> PDSHIFT] & PTE_V) && (((Pte *)(*vpt))[i >> PGSHIFT] & PTE_V))
-		{
-			u_int a = (*vpt)[i >> PGSHIFT]; 
-			u_int b = (*vpt)[i >> PGSHIFT]; 
-			u_int c = (*vpt)[i >> PGSHIFT];
-			writef("%x %x %x ",a, b, c);
-			writef("%x\n", VPN(UTOP-2*BY2PG));
-			writef("%x\n", VPN(UTOP-2*BY2PG));
-			duppage(newenvid, VPN(i));
-		}
-	}
-	ret = syscall_mem_alloc(newenvid, UXSTACKTOP - BY2PG, PTE_V | PTE_R);
-	if (ret < 0)
-	{
-		user_panic("fork alloc mem faild");
-	}
-	ret = syscall_set_pgfault_handler(newenvid, __asm_pgfault_handler, UXSTACKTOP);
-	if (ret < 0)
-	{
-		user_panic("fork set pgfault faild");
-	}
-
-	ret = syscall_set_env_status(newenvid, ENV_RUNNABLE);
-	if (ret < 0)
-	{
-		user_panic("fork set status faild");
-	}
-
-	return newenvid;
-}
-
-// Challenge!
-int
-sfork(void)
-{
-	user_panic("sfork not implemented");
-	return -E_INVAL;
-}