paramete.spad line 1 [edit on github]
ParametricPlaneCurve is used for plotting parametric plane curves in the affine plane.
coordinate(c, i) returns a coordinate function for c using 1-based indexing according to i. This indicates what the function for the coordinate component i of the plane curve is.
curve(c1, c2) creates a plane curve from 2 component functions c1 and c2.