% --- start of displayed preamble in the book ---

% --- start of displayed preamble in the book ---

vardef hilbertPath(expr s, n) =
save pa,pb,pc,A,B,C,shift,hilb,h;
path pa,pb,pc,hilb,h; pair A,B,C,shift;
if n=0: hilb=origin;
else: shift=(s, 0);
h=hilbertPath(s, n-1);
pa=h reflectedabout(origin,(1, -1));
A=point length(pa) of pa;
pb=h shifted (A+shift);
B=point 0 of pb;
hilb=pa & A--B & pb;
C=B shifted ((A+.5shift) rotated -90);
pc=reverse hilb reflectedabout(C,C+right);
hilb:=hilb & point length(hilb) of
hilb--point 0 of pc & pc;
fi
hilb
enddef;
% --- end of displayed preamble in the book ---
defaultfont:="ptmr8r";
warningcheck:=0;
beginfig(1)
side=5cm; n=5;
onestep=side/(2**n);
draw hilbertPath(onestep, n);
draw unitsquare scaled side
shifted (-.5onestep,.5onestep-side);
endfig;
end;