Function: substvec
Section: polynomials
C-Name: gsubstvec
Prototype: GGG
Help: substvec(x,v,w): in expression x, make a best effort to replace the
 variables v1,...,vn by the expression w1,...,wn.
Doc: $v$ being a vector of monomials of degree 1 (variables),
 $w$ a vector of expressions of the same length, replace in the expression
 $x$ all occurrences of $v_{i}$ by $w_{i}$. The substitutions are done
 simultaneously; more precisely, the $v_{i}$ are first replaced by new
 variables in $x$, then these are replaced by the $w_{i}$:
 \bprog
 ? substvec([x,y], [x,y], [y,x])
 %1 = [y, x]
 ? substvec([x,y], [x,y], [y,x+y])
 %2 = [y, x + y]     \\ not [y, 2*y]
 @eprog\noindent As in \kbd{subst}, variables may be replaced
 by a vector of values, in which case the cartesian product is returned:
 \bprog
 ? substvec([x,y], [x,y], [[1,2], 3])
 %3 = [[1, 3], [2, 3]]
 ? substvec([x,y], [x,y], [[1,2], [3,4]])
 %4 = [[1, 3], [2, 3], [1, 4], [2, 4]]
 @eprog
