Search found 844 matches

by wtf
Fri Sep 11, 2015 5:19 am
Forum: Logic and Philosophy of Mathematics
Topic: Proving that the difference between any two anagram numbers is always a multiple of nine
Replies: 59
Views: 6081

Re: Proving that the difference between any two anagram numbers is always a multiple of nine

Here's the proof that the difference of anagrams is divisible by 9. First, note that x = x0 + x1 * 10 + x2 * 10^2 + ... + xn * 10^n (writing xn or sometimes x_n to mean "x_subscript_n") and likewise y = y0 + y1 * 10 + y2 * 10^2 + ... + yn * 10^n. Note that since the x_i's are just a rearrangement of...
by wtf
Thu Sep 10, 2015 12:22 am
Forum: Logic and Philosophy of Mathematics
Topic: Is infinity all black and white?
Replies: 5
Views: 1126

Re: Is infinity all black and white?

@PhilX, I resurrected this months-old thread because you have a lot of similar questions about transfinite cardinals in this and other threads and I wanted to unpack some of these issues if you're still interested. The question of whether every infinite set is cardinally equivalent to an Aleph is ac...
by wtf
Tue Sep 08, 2015 11:54 pm
Forum: Logic and Philosophy of Mathematics
Topic: Differential calculus defined by differences - what more meaningful ?
Replies: 12
Views: 1496

Re: Differential calculus defined by differences - what more meaningful ?

A quick Google search will show that this author is a well-known crank. Regarding calculus, he clearly has never seen the proper formalization of the concept of a limit. He has an Amazon book if anyone wants to send him money.
by wtf
Tue Sep 08, 2015 11:43 pm
Forum: Logic and Philosophy of Mathematics
Topic: Does the center of a disk exist?
Replies: 22
Views: 3259

Re: Does the center of a disk exist?

a) Case of a physical disk. You can't precisely find or define the center to arbitrary precision because of measurement error. And any physical rotational mechanism is imperfect and has some amount of wobble. So there is no stationary point in a physical spinning disk. b) Case of a mathematical disk...