Recent content by fishturtle1

  1. F

    T_{0} - Space Equivalent Definition

    I think I got the definition wrong. It should be (i think) ##(X,\tau)## is ##T_0## if for any distinct points ##x,y \in X##, we can find an open set ##U## such that ##x \in U## and ##y \notin U## or ##x \notin U## and ##y \in U##. So in post #2, we can't guarantee there is an open set...
  2. F

    T_{0} - Space Equivalent Definition

    Sorry for the really dumb question, but is there an example where we can't replace the statement with: ##(X, \tau)## is ##T_0## if and only if for all ##x \in X##, ##\lbrace x \rbrace'## is empty? (I know ##\emptyset## is closed but...) Definition: ##(X,\tau)## is ##T_0## if for any distinct...
  3. F

    Prove that ## \sum_{d\mid n}\sigma_{1}(d)\sigma_{1}(\frac{n}{d}) ##

    The above should be ##(N \cdot N)(n) = \ldots = (N\sigma_0)(n)##. (why?) I think this is a right idea but there is a lot being used without explicit mention, which i think maybe makes it hard to follow. Somewhere we might mention "We will write the Dirichlet product of two arithmetic functions...
  4. F

    Inclusion/Exclusion Principle for 3 events

    I have a little trouble following it, but it looks like you've made a mistake in distribution e.g., ##(A \cup B) \cup Z \neq (A \cup Z) \cap (B \cup Z)## in general. We have ##P(Y \cup Z) = P(Y) + P(Z) - P(Y \cap Z)##. We can then apply I/E to ##P(Y)## (i'll leave that to you). We can also use...
  5. F

    Verify that the integers 1949 and 1951 are twin primes

    I had not thought of that. Rereading this thread, I completely agree with the points made by Mark and Perok and hope the OP understands them. I think i was mainly just reacting to some of the things in post #4. Apologies and hopefully the thread gets back on track.
  6. F

    Verify that the integers 1949 and 1951 are twin primes

    What's wrong with it? In the OP, they use the theorem that to show ##n## is prime, it is sufficient to show all primes ##p \le \sqrt{n}## do not divide ##n##. In fact, I really don't see anything wrong with the OP. Maybe other than writing something like ##\lfloor \sqrt{1949} \rfloor = 44##.
  7. F

    Proof: Twin Primes Always Result in Perfect Squares

    Looks good to me. Stylistically, one might write "Thus, ##p(p+2)+1## is a perfect square." instead of "Thus, ##(p+1)^2## is a perfect square.".
  8. F

    Prove that if ## n>2 ##, then there exists a prime ## p ## satisfying....

    ok so far. I'd rewrite the last two sentences as "Choose ##p = n! - 1##. Then ##n < p < n!## since ##n > 2##. Since the argument below shows such a prime ##n < p## exists, you shouldn't assume its existence here. The above sentence should be "Let ##p## be a prime factor of ##n! - 1##". We don't...
  9. F

    Prove that if ## n>2 ##, then there exists a prime ## p ## satisfying....

    It's not clear to me why such a prime ##p## exists. (referring to " Let ## p ## be a prime factor of ## n!-1 ## such that ## n<p ## for some ## n\in\mathbb{N} ## where ## n>2 ##." which won't quote for some reason). Here is where you've shown such a prime ##p## exists. Looks good to me. But...
  10. F

    Book on how to define ideas rigorously

    Topology through Inquiry by Starbird and Su.
  11. F

    For ## n\geq 2 ##, ## \sqrt[n]{n} ## is irrational?

    How do you prove 3. without something 'Write ##x =a/b## with ##\gcd(a, b) = 1##. Then ##xb^n = a^n##. ...'
  12. F

    Python "ImportError: bad magic number ...."

    Sorry... I just read the course page and it says I should be using python 3.5. Running the above code in Python 3.5. gets rid of the error. (and gives a new one! but hopefully i can fix that.)
  13. F

    Python "ImportError: bad magic number ...."

    # Test suite for Problem Set 3 (Simulating Robots) # Fall 2016 import sys import threading import traceback import unittest import random import imp test = imp.load_compiled("test", "test.pyc") import ps3 def xyrange(x_upper_bound, y_upper_bound): """ Returns the cartesian product of...
  14. F

    Comp Sci Creating a City Graph with Nodes & Edges

    Now it works, I forgot to return g in the buildCityGraph. class Node(object): def __init__(self, name): self.name = str(name) def get_name(self): return self.name def __str__(self): return self.name class Edge(object): def __init__(self, src, dest)...
Back
Top