Sometimes editing a thread title is an issue, but the issue is with vBulletin. If you ever want to change a thread title, and can't, just let me know...
Perhaps there are differences in terminology...I was taught that a function is concave up on an interval when its second derivative is positive, and...
No the link was meant to be HTTPS. I was thinking that you might have the HTTP site bookmarked and could be posting through that somehow but honestly...
Head of Mathematics Department, I.E.S. Sta Teresa, Madrid.
Prof. of Mathematical Methods, Univ. Alfonso X El Sabio, Madrid.
(Up until the 2008/2009 academic year. I am now devoted to investigation).