LIB1DIR = lib1-dir
LIB2DIR = lib2-dir

all: both

$(LIB1DIR):
	mkdir $(LIB1DIR)

$(LIB2DIR):
#	mkdir $(LIB2DIR)

lib1: lib1-build
	touch lib1

lib1-build: $(LIB2DIR) $(LIB1DIR) Nothing
	sleep 5s
	touch lib1-build

lib2: lib2-build
	touch lib2

lib2-build: $(LIB2DIR)
	sleep 15s
	touch lib2-build

a:
b:
c:
d:
e:
f:
g:
h:
i:
j:
k:
l:
m:
n:
o:
p:
q:
r:
s:
t:
u:
v:
w:
x:
y:
z:

both: lib1-build a b c d e f g h i j k l m n o p q r s t u v w x y z lib2-build
	$(MAKE) both-build
	touch both

both-build:
	sleep 2s
	touch both-build

clean:
	rm -rf [a-z]*

# This make sure that all variables in this file are exported to the
# environment for each command.
.EXPORT_ALL_VARIABLES:

# This avoids make deleting intermediate files in our implicit rules,
# such as ...configure and ...Makefile, which are needed in later builds.
.SECONDARY: