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2.2.22 Ring Mapping Example
If R is the current ring and E is an object in another ring, then the
function
Image
may be used to map E into R by substituting
polynomials from R for the indeterminates in E. (Also: see the
command
BringIn
for a shortcut in certain cases.)
example
Use S ::= Q[a,b,c];
I := Ideal(a^2+b^2,ab-c^2);
Use R ::= Q[x,y]; -- the current ring is R
F := RMap(x+y,x-y,y^2); -- define a map F:S --> R sending a to x+y,
-- b to x-y, and c to y^2
Image(I,F); -- the image of I under F
Ideal(2x^2 + 2y^2, -y^4 + x^2 - y^2)
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