The trisectrix of
Longchamps curve is a cubic ^{1)},
which is also
named the (equilateral) trefoil.
The curve is an epi spiral.
Longchamps studied the curve in 1888.
notes
1) With equation x (x^{2}  3y^{2}) = x^{2} + y^{2}.
2) To be distinguished from the quartic trefoil
