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Primary sources are directly from the Tax code, IRS or Court System. They have the authority to make laws. Secondary sources are anything else that someone writes about the primary sources. So for your items:
C. temp regs are primary because they are written by IRS
D. Revenue rulings are also primary because they are written by the IRS
E. General counsel memoranda 1988 is also written by IRS and primary
F. tax court memorandum - primary because courts have authority
H. Legislative regulations - Primary
I. letter ruling - primary
J. district court decision - secondary. Only the Federal tax court has authority.
K. small cases division of US tax court - primary since US tax court has authority
L. house ways and means committee report - neither. Congress has the authority to make laws, but the committee report is not authority.
M. tams are primary. Issued by IRS
N. proposed regs are also primary - issued by the IRS
Some primary sources have more weight than others, but if it comes directly from Congress, IRS or the tax court they have authority. Secondary sources are everything else. IRS website has a good summary. Here is the link:http://www.irs.gov/taxpros/article/0,,id=98137,00.html