Patamon's process of showing that a sequence of rigid transformations maps one triangle onto another, given a pair of congruent angles between two pairs of congruent sides, justifies the SAS congruence theorem.
Therefore, the correct answer is: A. the SAS congruence theorem.
The SAS (Side-Angle-Side) congruence theorem states that if two sides and the included angle of one triangle are congruent to two sides and the included angle of another triangle, then the two triangles are congruent.