Here is the PDF:<p><a href="https:&#x2F;&#x2F;mechanism.ucsd.edu&#x2F;teaching&#x2F;models&#x2F;levins.modelbuilding.pdf" rel="nofollow">https:&#x2F;&#x2F;mechanism.ucsd.edu&#x2F;teaching&#x2F;models&#x2F;levins.modelbuild...</a>