On the congruence that guarantees the rabbet of the parts: *triangles FEH and JBC are congruentes therefore rectangular and have congruentes sides EH and BC (opposing sides of rectangle), congruentes angles FEH and JBI (angles with parallel sides) *triangles LAB and MJI are congruentes therefore rectangular with congruentes sides AB and JI (congruentes AB and BC, and BC in turn congruente to the JI, since for transitividade triangles JBI and CEB are congruentes) and congruentes angles ABL and JIM (angles with parallel sides) |
The verification of the congruences in guarantees them that the clippings made in squares ABCD and ECGF, in fact, allow to mount square biggest BEHI.