diff --git a/Makefile b/Makefile
index 3a70f82482dc4e2ae5a464d2acfc3fe5c2c7995d..da0efa6493cb3354286c89915ec5a10928f41c69 100644
--- a/Makefile
+++ b/Makefile
@@ -33,9 +33,9 @@ TEXSRC	=	$(wildcard *.tex)
 SHELL	= /bin/bash
 LATEX	= latex -src
 BIBTEX	= bibtex
-DVIPS	= dvips 
+DVIPS	= dvips
 PDFPS	= pdftops
-PDF	= max_print_line=1000 pdflatex -shell-escape -src -halt-on-error -synctex=1 -interaction nonstopmode -file-line-error-style 
+PDF	= max_print_line=1000 pdflatex -shell-escape -src -halt-on-error -synctex=1 -interaction nonstopmode -file-line-error-style
 OPEN    = xdg-open
 
 # Mac-specific definitions
@@ -56,9 +56,9 @@ pdf : $(PDFNAMES) 			# Compile pdf's
 over : clean pdf			# Force recompile
 
 .PHONY: clean
-clean : 
+clean :
 	@echo Soft clean
-	-rm *.blg *.log *.out $(DVINAMES) $(PDFNAMES) 2>/dev/null ; true 
+	-rm *.blg *.log *.out $(DVINAMES) $(PDFNAMES) 2>/dev/null ; true
 
 .PHONY: cleanall
 cleanall : clean
@@ -66,7 +66,7 @@ cleanall : clean
 	-rm *~ *.aux *.bbl *.lof *.lot *.toc *.ps *.cit *.synctex.gz 2>/dev/null ; true
 
 .PHONY: cleanaux
-cleanaux : 
+cleanaux :
 	-rm *.blg *.log *.out *.dvi*.aux *.bbl *.lof *.lot *.toc *.ps *.cit *.synctex.gz 2>/dev/null ; true
 
 .PHONY: show
@@ -77,7 +77,7 @@ show: $(PDFNAMES)
 edit: $(SRCNAMES)
 	for file in $(SRCNAMES); do $(OPEN) $$file; done
 
-%.bbl: $(BIBSRC) 
+%.bbl: $(BIBSRC)
 	@echo Recreate the .aux file
 	$(PDF) $(@:.bbl=.tex) >/dev/null || cat $(@:.bbl=.log)
 
@@ -91,23 +91,23 @@ edit: $(SRCNAMES)
 
 %.dvi: %.tex	# Cancel the default rule
 
-%.dvi: $(TEXSRC) $(wildcard $(THISDIR)*.tex) 
+%.dvi: $(TEXSRC) $(wildcard $(THISDIR)*.tex)
 	@echo If compilation fails manipuate the timestamp to prevent recognission of .dvi as ready
 	$(LATEX) $(@:.dvi=.tex) || (touch --date="`date -R -r $(@:.dvi=.tex)`" $@ & false)
-	
+
 	@echo If the citations were updated recompile the .bbl file
 	grep -o -G "Citation \`[^']*" $(@:.dvi=.log) | md5sum -c $(@:.dvi=.cit) || $(BIBTEX) $(@:.dvi=.aux)
-	
+
 	while grep -q "Rerun to get cross-references right." $(@:.dvi=.log); \
 	do $(LATEX) $(@:.dvi=.tex); done
-	
+
 	@echo Update the missing citation hash
 	grep -o -G "Citation \`[^']*" $(@:.dvi=.log) | md5sum > $(@:.dvi=.cit)
 
 %.pdf: %.tex	# Cancel the default rule
 
 %.pdf: $(TEXSRC) $(wildcard $(THISDIR)*.tex) %.bbl
-	@echo Compiling $@ 
+	@echo Compiling $@
 	($(PDF) $(@:.pdf=.tex) >/dev/null) || (touch --date="`date -R -r $(@:.pdf=.tex)`" $@ & cat $(@:.pdf=.log) & false)
 
 	@echo Recompile tikz images
@@ -115,7 +115,7 @@ edit: $(SRCNAMES)
 	then \
 	    $(MAKE) -e -f $(@:.pdf=.makefile); \
 	    $(PDF) $(@:.pdf=.tex) >/dev/null;  \
-        fi
+  fi
 
 	@echo Create $(@:.pdf=.cit) if it does not exist
 	test -s $(@:.pdf=.cit) || echo '' | md5sum > $(@:.pdf=.cit)
@@ -131,12 +131,12 @@ edit: $(SRCNAMES)
 	    $(PDF) $(@:.pdf=.tex) >/dev/null; \
 	else \
 	    echo "None"; \
-	fi 
+	fi
 
 	@echo Update the citation hash
 	grep -o -G "Citation \`[^']*" $(@:.pdf=.log) | md5sum > $(@:.pdf=.cit)
 
-%.ps : %.pdf 
+%.ps : %.pdf
 	$(PDFPS) -level1 $<  		# Create .ps from .pdf
 
 .PHONY: bib
@@ -180,6 +180,6 @@ up: $(PDFNAMES)
 
 # Check common text writting issues
 .PHONY: check
-check: 
+check:
 	-echo "Checking duplicates.."
 	-grep -Eon -r --include "*.tex" '(\b[[:alpha:]]+\b) \1\b' .
diff --git a/catprog.tex b/catprog.tex
index 5f4114375c15469f507d97dc7b284586ffe4edbc..adf7d4812b3014fc87c6773a530de5e9d4fa7eb4 100644
--- a/catprog.tex
+++ b/catprog.tex
@@ -135,7 +135,7 @@
 \providecommand{\dash}{\nobreakdash-\hspace{0pt}}			    % non-line-beaking hyphen
 \providecommand{\erule}{\rule{0pt}{0pt}}		        	    % Empty object whose emptiness is not recognized by LaTeX
 
-\providecommand{\by}[1]{\text{/\!/~#1}}			% Comments in equations
+\providecommand{\by}[1]{\text{/\!\!/~#1}}			% Comments in equations
 \providecommand{\pacman}[1]{}					% Hide a piece of text
 
 \providecommand{\noqed}{\def\qed{}}				% Undefine the QED symbol