25 setxunit
7.5 setborder
-6 6 setxrange
-6 6 setyrange
jpegmode
/a 3 def
/b 1 def
/c 0.5 def

2 2 settkstep
1 1 setsubtkstep
2 2 setmkstep
ticks
traceaxes
axesarrow
0.75 setlinewidth
continu
bleu
/X {settvar
#rpn#   (a-b)*1/(1.5-c)*cos(t) +(c/b)*cos((a-b)*t/b)
} def
/Y {settvar
#rpn#   (a-b)*sin(t) - (c/b)*sin((a-b)*t/b)
} def
 0 115 pi mul  {X} {Y} Courbeparam