D.15.25.2 preim

Usage:

preim(O, x); O list, x poly/number

Assume:

O is a list of ordering of the set of vertices (or indices of the vertices), x is a monomial representing a vertex of a graph (or the index of the vertex we are interested in).

Return:

int.

Theory:

This gives the entry number of x in list O.

LIB "tropicalEllipticCovers.lib";
ring r=0,(x1,x2,x3,x4),dp;
preim(list(x1,x3,x4,x2),x2);