See Section 27.10.6 for parametric equations in 3D geometry.
The parameq command finds a parametric equation for a curve.
Note that t must be a formal variable, it may be necessary to purge it with purge(t).
| parameq(line(-1,i)) |
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| parameq(circle(-1,i)) |
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| normal(parameq(ellipse(-1,1,i))) |
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