%!PS-Adobe-3.0

% The next line defines the number of "slices"
/n { 3 } def

% n i slice
/slice {
    newpath
    dup
    % n i i
    dup 0 exch
    % n i i 0 i
    180 0 arcn
    % n i
    2 copy 2 copy add
    % n i n i n+i
    3 1 roll sub
    % n i n+i n-i
    0 exch 180 0 arc
    % n i
    2 copy 2 copy add 1 add
    % n i n i n+i+1
    3 1 roll sub 1 sub
    % n i n+i+1 n-i-1
    0 exch 0 180 arcn
    % n i
    dup 1 add dup
    % n i i+1 i+1
    0 exch 0 180 arc
    gsave
    exch 1 sub div setgray fill
    grestore
    0 setgray stroke
} def

50 400 translate
200 n div dup scale
.005 n mul setlinewidth

0 1 n 1 sub {
    dup n exch slice
    dup
    n 1 sub div 1 sub neg setgray
    2 mul 1 add 0 .2 0 360 arc fill
} for

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