foo1: x1 x3 .WAIT x2
foo2: x2 .WAIT x3
foo3: x1 x2 x3
foo4: y1 y2 y3

1: A .WAIT B
2: B .WAIT C
3: C .WAIT A
4: C A

x2 x3 y1 y2 y3 A B C:
        echo $@ ; sleep 2 ; echo finished $@
x1:
        echo $@ ; sleep 4 ; echo finished $@

all: a b $(WAIT) c d s-e s-f
all2: a b c $(WAIT) d e $(WAIT) f g h $(WAIT) i $(WAIT) $(WAIT) j k
all3: a b sub3 i j
all4: a b sub4 i j

.PHONY: all1 all2 all3 sub3 clean

sub3: c d e f g h
.NOTPARALLEL: sub3

sub4: c .WAIT d .WAIT e .WAIT f .WAIT g .WAIT h

clean:
        rm -f [a-k] [stu]-*

a b c d e f g h i j k:
        @echo Starting update of $@; sleep 2; echo touch $@; echo Finished update of $@

s-%: u-% $(WAIT) t-%
        @echo Starting update of $@; sleep 2; echo touch $@; echo Finished update of $@

t-%:
        @echo Starting update of $@; sleep 2; echo touch $@; echo Finished update of $@

u-%:
        @echo Starting update of $@; sleep 2; echo touch $@; echo Finished update of $@