Thanks for your solution; it works just fine. I am not familiar with how you defined the pmatrix. Any links to manuals to learn such definitions? Also, this is the second thing I have tried to adapt from typesetting mathematics in plain TeX that didn’t work. I tried to draw commutative diagrams some time back using \diagram{…} which didn’t work(Got the idea from the book “A beginner’s book of TeX” pg. 161 by Seroul et al ). 

I guess what I am asking is that, what are the limits of what I can use out-of-the-box from Tex when typesetting mathematics? I have read Aditya’s ConTeXt-LaTeX tutorial which is fantastic. But the stuff illustrated there are quite limited. Are there any materials I can read on this?

Thanks for your help.