Complex sentence: The congruum itself is four times the area of the same Pythagorean triangle, so (as the area of a Pythagorean triangle) every congruum is a congruent number; conversely, every congruent number is a congruum multiplied by the square of a rational number.
Split into simpler sentences: The congruum itself is four times the area of the same Pythagorean triangle. Conversely, every congruent number is a congruum multiplied by the square of a rational number.