Examples 1.4.3(c):
Let A be the set N x N and define an equivalence
relation r on N x N and addition of the equivalence
classes as follows:
Since two pairs (a,b) and (a', b') are related if
- (a,b) is related to (a’,b’) if a + b’ = a’ + b
- [(a,b)] + [(a',b')] = [(a + a', b + b')]
- [(a,b)] * [(a’, b’)] = [(a * b’ + b * a’, a * a’ + b * b’)]
- a + b' = a' + b or b - a = b' - a'
- the symbol 2 denote the equivalence class [(1,3)] containing, for example, the pairs (1,3), (5,7), and (100, 102).
- the symbol -3 denotes the equivalence class [(4,1)], containing, for example, the pairs (4,1), (8,5), and (103, 100).
- 2 + -3 = [(1,3)] + [(103,100)] = [(1,2)] = -1
- 2 * (-3) = [(1,3)] * [(103,100)] = [(1,7)] = -6