% --- start of displayed preamble in the book --- def sierpinski(expr a,b,n)= if n=0: fill a--(b rotatedabout(a,60))--b--cycle; else: sierpinski(a,0.5[a,b],n-1); sierpinski(0.5[a,b],b,n-1); sierpinski(0.5[a,b rotatedabout(a,60)], 0.5[a rotatedabout(b,-60),b],n-1); fi enddef; % --- end of displayed preamble in the book --- defaultfont:="ptmr8r"; warningcheck:=0; beginfig(1) sierpinski((0,0),(0,6cm),6); endfig; end;