Marc van Dongen ([EMAIL PROTECTED]) wrote: : An integer $a$ divides integer $b$ if there exists an integer : $c$ such that $a c= b$.
[snip] : gcd 0 0 = 0; and : gcd 0 0 /= error "Blah" To make clear why $0$ (and not any other non-zero integer) is the gcd of $0$ and $0$ I should have added that for the integer case $g$ is called a greatest common divisor (gcd) of $a$ and $b$ if it satifies each of the following two properties: 1) $g$ divides both $a$ and $b$; 2) if $g'$ is a common divisor of $a$ and $b$ then $g'$ divides $g$. First notice that $0$ is a gcd of $0$ and $0$ because of the following: *) $0$ divides $0$ (and divides $0$); *) whenever $g'$ is an integer that divides $0$ and divides $0$ then $g'$ divides $0$. Next notice that if $g$ is any non-zero integer then $g$ cannot be a gcd of $0$ and $0$ because $0$ (a common divisor of $0$ and $0$) does not divide $g$. Finally, observe that this makes $0$ the unique gcd of $0$ and $0$. : The gcd of two integers is usually defined as a non-negative : number to make it unique. Regards, Marc van Dongen _______________________________________________ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell