Utilize the input text as a context reference, choose the right relationship between 'Walter Energy' and 'coal' from the options.
Options: platform, legal form, product/material produced, creator

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