prologues := 1;
tracingequations := 1;
beginfig(1);
   drawoptions(withcolor .7[black,white]);
   % equal-sided triangle
   y1 = y2;
   1 = x2 - x1;
   x3 = 0.5[x1, x2];
   (z3 - z1) rotated 60 = (z3 - z2);
   origin = 0.5[0.5[z1,z2], z3];
   %
   path triangle;
   triangle := z1 -- z2 -- z3 -- cycle;
   %
   w := 3in;
   penwidth := 1/12 w;
   %
   pickup pencircle scaled penwidth;
   draw triangle scaled w withcolor (1, 0, 0);
   % inner symbol
   y4 = y8; y5 = y9; y6 = y10; y7 = y11;
   x4 = x5; x6 = x7; x8 = x9; x10 = x11;
   0.5[x4,x8] = 0.5[x6,x10] = 0;
   x9 = 2 x10;
   0.5[y5,y6] = 1/3[y1,y3];
   %
   x4 = 3/8 [x1,x2];
   y4 = 1/8[y1,y3];
   z5 - z4 = z9 - z8 = z7 - z6 = z11 - z10;
   x6 - x5 = y6 - y5;
   %
   % pickup pencircle scaled 2pt;
   pickup penrazor scaled (2/3 penwidth);
   draw (z4 -- z5 -- z6 -- z7) scaled w withcolor (0, 0, 0);
   draw (z8 -- z9 -- z10 -- z11) scaled w withcolor (0, 0, 0);
endfig;
end.