Variable a is always one out of #u-about, #u-projects, #u-contact, #u-follow.
How to make the function not animate a?
function bla(a) {$('#u-about, #u-projects, #u-contact, #u-follow').animate(...);
You can use not() and pass a to not to exclude the element you do not want.
function bla(a) {$('#u-about, #u-projects, #u-contact, #u-follow').not(a).animate(...
not()
Given a jQuery object that represents a set of DOM elements, the .not() method constructs a new jQuery object from a subset of the matching elements. The supplied selector is tested against each element; the elements that don't match the selector will be included in the result, Reference
Use the .not() selector to exclude a particular variable or selector from a jQuery object.
$('#u-about, #u-projects, #u-contact, #u-follow').not(a).animation
a refers to an object, not to the anchor tag.