Refer to the input text as context and select the correct relationship between 'Walter Energy' and 'coal' from the available options.
Options: creator, platform, product/material produced, legal form

Walter Energy Inc.’s most senior lenders are pushing the unprofitable coal miner to slash worker pay, reduce pension expenses and idle plants as part of a bankruptcy plan that they will present the company this week, according to three people with direct knowledge of the matter.
product/material produced