David R. Hall 
Unity of Corinthian Correspondence [PDF ebook] 

The thesis of this book is that 1 and 2 Corinthians are closely related; that Paul faces the same opponents in both letters; that the letter written with many tears referred to in 2 Corinthians is 1 Corinthians; and that there is no need to posit an intermediate visit or letter between the two canonical letters. Throughout the two letters Paul implements a consistent pastoral strategy, and an understanding of this strategy explains the difference in tone between various sections of the two letters. There is no need for theories of partition.