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5.1.106 preimage
Syntax:
preimage ( map )
preimage ( ring_name, map_name, ideal_name )
preimage ( ring_name, ideal_expression, ideal_name )
Type:
- ring
ideal
Purpose:
- returns the source ring of a map (in the first case) or returns the preimage of
an ideal under a given map.
The second argument has to be a map from the basering to the given ring
(or an ideal defining such a map),
and the ideal has to be an ideal in the given ring.
Note:
- As
preimage is handling ideals (not polynomials), the result of a preimage
calculation of a principal ideal is (the closure of) the preimage of the ideal,
not that of the polynomial.
Example:
See
ideal;
kernel;
map;
ring.
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