Addition in ℤ/pℤ or in ℤ/pℤ[x] : +

5.34.2 Addition in ℤ/pℤ or in ℤ/pℤ[x] : +

+ adds two integers in ℤ/pℤ, or two polynomials in ℤ/pℤ[x]. For polynomial expressions, use the normal command to simplify.
For integers in ℤ/pℤ, input :

3%13+10%13

Output :

0%13

For polynomials with coefficients in ℤ/pℤ, input :

normal((11*x+5 )% 13+(8*x+6)%13)

normal(11% 13*x+5%13+8% 13*x+6%13)

Output :

(6%13)*x+-2%13