Euclid's Elements: Book 1, Prop 26

A step by step board presentation of Book 1, Proposition 26, our ASA or AAS proof for equal triangles: "If two triangles have two angles equal to two angles respectively, and one side equal to one side, namely, either the side adjoining the equal angles, or that subtending one of the equal angles, then the remaining sides equal the remaining sides and the remaining angle equals the remaining angle."