I have been advised how to add additional contact info fields to the User admin area here (Click here).

However, I am not entirely sure how I can display the the field contents in a link within my template files.

Here is the code in my functions.php:

add_filter( 'user_contactmethods', 'more_contactmethods' );
function more_contactmethods( $contactmethods ) {
    $contactmethods['twitter'] = 'Twitter URL';
    $contactmethods['facebook'] = 'Facebook URL';
    $contactmethods['linkedin'] = 'LinkedIn URL';
    return $contactmethods;
}


And here's the code in one of my template files, but it doesn't seem to work, so I wonder whether I can actually do it this way?

&lt;?php 
    $twitter = get_usermeta( $user_id, 'facebook' ); 
    $facebook = get_usermeta( $user_id, 'twitter' );
    $linkedin = get_usermeta( $user_id, 'linkedin' );
?&gt;

    &lt;a href="&lt;?php echo $twitter ?&gt;" id="twitterBtn" title="Visit our Twitter page"&gt;Visit our Twitter page&lt;/a&gt;



Question: Group isomorphisms and a possible trivial statement?
Answer: Every group of three elements is isomorphic to one another, and is cyclic. Put differently, there is only one group of order $3$ up to isomorphism.

This is not true of groups of order four, of which there are two, up to isomorphism: The group $(\mathbb Z_4, +)$ and the Klein 4-group $\{e, a, b, c\} = \mathbb Z_2\times \mathbb Z_2$, in wich every element is of order $2$.