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# Laws valid for the positive rationals

```
The positive rational numbers (numbers given by n+a/b where n, a
and b are positive integers) were the numbers used for centuries,
up to the time of the invention of 0.  What are the algebraic
rules that are followed by the positive rationals?  They obey
the following laws:

Let S be the set of all positive rational numbers.  For every
a,b,c in set S:

a,b in S implies a+b in S

a+(b+c) = (a+b)+c

a+b = b+a

a+x = b+x implies a=b

7.  Closed under Multiplication.
a,b in S implies ab in S

8.  Associative Law under Multiplication.
a(bc) = (ab)c

9.  Identity Element under Multiplication.
1a =a1 = a

10.  Inverse exists for every element under Multiplication.
aa' = a'a = 1    where a' is the inverse of a

11.  Commutative Law under Multiplication.
ab = ba

12.  Cancellation Law under Multiplication.
ax = bx implies a=b

13.  Left Distributive Law -- Multiplication over Addition
a(b+c) = ab + ac

14.  Right Distributive Law -- Multiplication over Addition
(a+b)c = ac + bc

Note that there is no identity element under addition.  And no
inverse elements exist under addition.  To get an identity
element, zero had to be appended to the positive rationals.  To
get inverse elements, negative numbers had to be appended.

The reason the most of these laws hold is intuitively obvious
when viewed in the right way.  In the case of addition we can
think in terms of adding sets of objects.  In the case of
multiplication we can view the product "ab" as an area and
the product "abc" as a volume to confirm that the associative,
commutative, and distributive laws hold.

```