09.12.2012 Views

Concrete mathematics : a foundation for computer science

Concrete mathematics : a foundation for computer science

Concrete mathematics : a foundation for computer science

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

60 SUMS<br />

In fact, our definition of infinite sums is quite simple. Let K be any<br />

set, and let ok be a real-valued term defined <strong>for</strong> each k E K. (Here ‘k’<br />

might actually stand <strong>for</strong> several indices kl , k2, . . , and K might there<strong>for</strong>e be<br />

multidimensional.) Any real number x can be written as the difference of its<br />

positive and negative parts,<br />

x .= x+-x where x+ =x.[x>O] and x- = -x.[x 0 and each term ok is nonnegative. The proof

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!