-$pdflatex = 'lhs2TeX -v --poly < cλash.lhs > cλash.tex; pdflatex -file-line-error -halt-on-error -synctex=1 cλash.tex cλash.pdf';
-$clean_ext = "synctex.gz ptb tex";
\ No newline at end of file
+$pdflatex = 'lhs2TeX -v --poly < cλash.lhs > cλash.tex; pdflatex -file-line-error -halt-on-error -synctex=1 --enable-write18 cλash.tex cλash.pdf';
+$clean_ext = "synctex.gz ptb tex";