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D.4.2.7 is_surjective

Procedure from library algebra.lib (see algebra_lib).

Usage:
is_surjective(phi); phi map to basering, or ideal defining it

Return:
an integer, 1 if phi is surjective, 0 if not

Note:
The algorithm returns 1 if and only if all the variables of the basering are contained in the polynomial subalgebra generated by the polynomials defining phi. Hence, it tests surjectivity in the case of a global odering. If the basering has local or mixed ordering or if the preimage ring is a quotient ring (in which case the map may not be well defined) then the return value 1 needs to be interpreted with care.

Example:
 


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