25 setxunit
7.5 setborder
-6 6 setxrange
-6 6 setyrange
jpegmode
/a 7 def
/b 3 def
/c 2 def

2 2 settkstep
1 1 setsubtkstep
2 2 setmkstep
ticks
traceaxes
axesarrow
0.75 setlinewidth
continu
bleu
/X {settvar
#rpn#   (a-b) * Cos (t) + c * Cos (t*(-1+a/b))
} def
/Y {settvar
#rpn#   (a-b) * Sin (t) - c * Sin (t*(-1+a/b))
} def
  0  15 pi mul {X} {Y} Courbeparam