Function: Map
Section: conversions
C-Name: gtomap
Prototype: DG
Help: Map({x}): converts the matrix [a_1,b_1;a_2,b_2;...;a_n,b_n] to the map a_i->b_i.
Description:
 ():list           mkmap()
 (gen):list        listinit(gtomap($1))
Doc: A ``Map'' is an associative array, or dictionary: a data
 type composed of a collection of (\emph{key}, \emph{value}) pairs, such that
 each key appears just once in the collection. This function
 converts the matrix $[a_1,b_1;a_2,b_2;\dots;a_n,b_n]$ to the map $a_i\mapsto
 b_i$.
 \bprog
 ? M = Map(factor(13!));
 ? mapget(M,3)
 %2 = 5
 @eprog\noindent If the argument $x$ is omitted, creates an empty map, which
 may be filled later via \tet{mapput}.
