"Indirect Inference," symmetry. Premise that only a judge's reasoning. Mainly: (1) determine the nature of the premise is a direct inference, including for quality law, conversion method, for quality digital method. (2) provided that a judge's direct inference relations. Such as: "a ratio of b large, so, b than a little." (3) provided that a false statement to judge the direct inference. If by "if the two triangles congruent, then their corresponding angle equal to" push "the corresponding angle of only two triangles are equal, only the two triangles congruent."