Before revision: Ferguson has an extensive bibliography and points out that a similar (but different) problem had been considered by Arthur Cayley in 1875 and even by Johannes Kepler long before that .
After revision: , who spent 2 years investigating 11 candidates for marriage during 1611 -- 1613 after the death of his first wifeFerguson has an extensive bibliography and points out that a similar (but different) problem had been considered by Arthur Cayley in 1875 and even by Johannes Kepler long before that .