You say 'abs x = x/2', but what's that (/)? For example, what is 'abs' supposed to give when called on (the representation of) the polynomial X^2 + 3X + 2?<div><br /></div><div><br /></div>Interesting also to think about what the meaning of 'n*(n+1)/2' on polynomials should even be. What is the sum of the numbers (polynomials?) from 1 to X + 1?<div><br /></div><div><br /></div>- Tom<div><br /></div><div><br /></div>-------- Original Message --------<div><br /></div>On 16 Dec 2020, 23:48, Henning Thielemann &lt; lemming@henning-thielemann.de&gt; wrote:<div><br /></div><div><br /></div>On Wed, 16 Dec 2020, Tom Smeding wrote:<div><br /></div>&gt; I'm not sure what "sound" means if the documentation[1] for Num states that the only reasonable expectation is<div><br /></div>&gt; that of a ring.<div><br /></div>&gt;<div><br /></div>&gt; However, if we are to have laws for signum and abs, then I would expect that 'abs n = n * signum n'. My<div><br /></div>&gt; definitions satisfy that law.<div><br /></div>What about abs x = x/2 and signum _ = 2?<div><br /></div>Would satisfy your law and solve the problem of the original poster.<div><br /></div>