all: out1 out2 out3 out4 nl1 nl2 nl3 nl4 

N= grep -v '^ *$$'

nl1 : ex1.pl 
	nl ex1.pl > nl1
nl2 : skelgen.pl 
	nl skelgen.pl > nl2
nl3 : ex3.pl 
	nl ex3.pl > nl3
nl4 : ex4.pl 
	nl ex4.pl > nl4

out1 : art1.xml	ex1.pl
	ex1.pl art1.xml | $N | nl > out1
out2 : art1.xml	skelgen.pl
	skelgen.pl art1.xml| nl   > out2
out3 : art1.xml art2.xml art3.xml proc.xml ex3.pl
	ex3.pl proc.xml |$N| nl  > out3
out4 : art1.xml art2.xml art3.xml proc.xml ex4.pl
	ex4.pl proc.xml  |$N| nl > out4