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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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