References
- Ballantine , C. S. 1978 . Product of idempoitent matrices . linear Alg & Appl , 19 : 81 – 86 .
- Erdos , J. A. 1967 . On products of idempotent matrices . Glasgow Math J , 8 : 118 – 122 .
- Laffey , T.J. 1983 . Linear & Multilinear Algebra , 14 : 309 – 314 .