Zn = {0, 1, ..., n - 1} a, b " Zn a •"n b
a + b n
"a, b, c " Zn a •"n (b •"n c) = (a •"n b) •"n c
"a, b " Zn a •"n b = b •"n a
"a " Zn "b " Zn a •"n b = 0
Zn = {0, 1, ..., n - 1} a, b " Zn a n b
a · b n
"a, b, c " Zn a n (b n c) = (a n b) n c
"a, b " Zn a n b = b n a
n a, b " Zn a, b = 0 a n b = 0

n
X f, g " XX
f ć% g f g
(f ć% g) ć% h = f ć% (g ć% h)
S
ABC
S
S
e " S a " S a · e =
e · a = a
a " S b " S a · b = b · a = e
T