
4.11.3 map operations
( )
 composition of maps. If, for example,
f and g are maps,
then f(g) is a map expression giving the composition
of f and g ,
provided the target ring of g is the basering of f .
 map_expression
[ int_expressions ]
 is a map entry (the image of the corresponding variable)
Example:
 ring r=0,(x,y),dp;
map f=r,y,x; // the map f permutes the variables
f;
==> f[1]=y
==> f[2]=x
poly p=x+2y3;
f(p);
==> 2x3+y
map g=f(f); // the map g defined as f^2 is the identity
g;
==> g[1]=x
==> g[2]=y
g(p) == p;
==> 1

