Any nondegenerate closed space curve may be nondegenerately deformed into either of the two curves illustrated above. Neither of these can be nondegenerately transformed into the other.
Feldman's Theorem
Explore with Wolfram|Alpha
References
Feldman, E. A. "Deformations of Closed Space Curves." J. Diff. Geom. 2, 67-75, 1968.Pohl, W. F. "The Self-Linking Number of a Closed Space Curve." J. Math. Mech. 17, 975-985, 1968.Referenced on Wolfram|Alpha
Feldman's TheoremCite this as:
Weisstein, Eric W. "Feldman's Theorem." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/FeldmansTheorem.html