Function: zetamultdual
Section: transcendental
C-Name: zetamultdual
Prototype: G
Help: zetamultdual(s): s being either an evec, avec, or index m,
 return the dual sequence in avec format.
Doc: $s$ being either an \kbd{evec}, \kbd{avec}, or index \kbd{m},
 return the dual sequence in \kbd{avec} format.
 The dual of a sequence of  length $r$ and weight $k$ has length $k-r$ and
 weight $k$. Duality is an involution and zeta values attached to
 dual sequences are the same:
 \bprog
 ? zetamultdual([4])
 %1 = Vecsmall([2, 1, 1])
 ? zetamultdual(%)
 %2 = Vecsmall([4])
 ? zetamult(%1) - zetamult(%2)
 %3 = 0.E-38
 @eprog
 In \kbd{evec} form, duality simply reverses the order of bits and swaps $0$
 and $1$:
 \bprog
 ? zetamultconvert([4], 0)
 %4 = Vecsmall([0, 0, 0, 1])
 ? zetamultconvert([2,1,1], 0)
 %5 = Vecsmall([0, 1, 1, 1])
 @eprog
