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7.3.21 preimage (plural)

Syntax:
preimage ( ring_name, map_name, ideal_name )
preimage ( ring_name, ideal_expression, ideal_name )
Type:
ideal
Purpose:
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:
To compute the kernel of a map, the preimage of zero has to be determined. Hence there is no special command for computing the kernel of a map in PLURAL.
Remark:
In the non-commutative case, it is implemented only for maps -> , where is a commutative ring.
Example:
 
See ideal (plural); map (plural); ring (plural).


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