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defaultfont:="ptmr8r";
warningcheck:=0;
beginfig(1)
numeric r,pr,x,rmin,rmax,ur,ux;
rmin=1.9;
rmax=3;
ur=5cm;
ux=6cm;
r:=rmin;
pr:=(rmax-rmin)/250;
for i=1 upto 250:
x:=.3;
for j=1 upto 50:
x:=(1+r)*x-r*x*x;
endfor;
for j=1 upto 50:
x:=(1+r)*x-r*x*x;
draw (r,x) xscaled ur yscaled ux;
endfor;
r:=r+pr;
endfor;

endfig;
end;