The Problems of Congruent Numbers and Concordant Forms
Eric Temple Bell · Proceedings of the National Academy of Sciences · 1947
1. Four Related Problems. - All letters in formulas denote rational integers, and solution means the complete solution in such integers. The problem of solving the simultaneous diophantine equations rX^2 + mY^2 = rZ^2, sX^2 + nY^2 = sW^2 includes as special cases two classical problems.