1.- What does the so-called Estrada Doctrine consist of, in the terms in which it was originally formulated in 1930? 2.- What is the antecedent of the Estrada Doctrine, prior to the Mexican Revolution? 3.- Are the Estrada Doctrine and the principle of non-intervention the same? 4.- Does the Estrada Doctrine, in the terms in which it was originally formulated, maintain its validity at the present time, in light of the principles of Mexico's foreign policy, as they appear today in article 89, fraction X constitutional?