PolynomialMod[poly, m] for integer m gives a polynomial in which all coefficients are reduced modulo m.
When m is a polynomial, PolynomialMod[poly, m] reduces poly by subtracting polynomial multiples of m, to give a result with minimal degree and leading coefficient.
PolynomialMod gives results according to a definite convention; other conventions could yield results differing by multiples of m.
EXAMPLES
Basic Examples 
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