I am typing up solutions to a variety of problems in a textbook, and I want to use the proof environment for proofs but a similar environment for solutions. The link here
shows how I can make my own solution environment, but I want the indication for the end of a solution to be slightly different than that of a proof. I'd like solutions to end with the QED as \blackbox whereas I want the proof environment to stay as it is (white box to indicate QED). Is there an easy way to make this happen?