  FRONTPAGE = $(wildcard $(FRONTPAGE_DIR)/*)
  FRONTPAGE_DEP = $(patsubst %, build/%, $(FRONTPAGE))
  
  IMG_NOTEBOOK = $(filter-out $(FRONTPAGE_DIR), $(wildcard img/*))
  ORIGIN_DEPS = $(IMG_NOTEBOOK) $(wildcard data/*) environment.yml README.md
  DEPS = $(patsubst %, build/%, $(ORIGIN_DEPS))
  
  PKG = build/_build/html/d2l-zh.zip
  
  pkg: $(PKG)
 
</s> remove # Copy everything to build/.
 </s> add # Copy XX to build/XX if build/XX is depended (e.g., $(DEPS))
ORIGIN_DEPS = $(IMG_NOTEBOOK) $(wildcard data/* gluonbook/*) environment.yml README.md
  FRONTPAGE = $(wildcard $(FRONTPAGE_DIR)/*)
  FRONTPAGE_DEP = $(patsubst %, build/%, $(FRONTPAGE))
  
  IMG_NOTEBOOK = $(filter-out $(FRONTPAGE_DIR), $(wildcard img/*))
ORIGIN_DEPS = $(IMG_NOTEBOOK) $(wildcard data/* gluonbook/*) environment.yml README.md
  DEPS = $(patsubst %, build/%, $(ORIGIN_DEPS))
  
  PKG = build/_build/html/d2l-zh.zip
  
  pkg: $(PKG)
keep keep keep keep replace keep keep keep keep keep
 cp gluonbook in Makefile, add load_timemachine in gb 
Makefile