View source for Flecnode

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''on a planar curve''

A point at which a node (or double point; cf. also [[Node]]) and an inflection (cf. also [[Point of inflection]]) coincide.

Thus, one of the tangents at the node has intersection multiplicity at least $4$ with the curve at that point.

====References====
<table>
<TR><TD valign="top">[a1]</TD> <TD valign="top">  J.W. Bruce,   "Lines, surfaces and duality"  ''Math. Proc. Cambridge Philos. Soc.'' , '''112'''  (1992)  pp. 53–61</TD></TR>
<TR><TD valign="top">[a2]</TD> <TD valign="top">  M. Tsuboko,   "On the line complex determinant of flecnode tangents of a ruled surface and its flecnodal surfaces"  ''Memoirs Ryojun Coll. Engin.'' , '''11'''  (1938)  pp. 233–238</TD></TR>
</table>