st: Program codes of the built-in commands in STATA

["Sanzidur Rahman" <sanzidur.rahman@plymouth.ac.uk>]

Dear all:
 
How can I access the details of underlying program codes of the built-in commands in STATA? I urgently need access to TWO OF THE BUILT-IN commands. 
 
Stochastic Production/Cost Frontier
Heckman's Model (both the two-stage approach as well as the single stage MLE procedure)
 
Thank you all in anticipation.
 
Best wishes.
 
Sanzid  

*
*   For searches and help try:
*   http://www.stata.com/support/faqs/res/findit.html
*   http://www.stata.com/support/statalist/faq
*   http://www.ats.ucla.edu/stat/stata/