import problem sets for Esty Proof Book
Fixed bug in which the problem doesn't accept the answers in either order.
Replace \left by \left( in solution
Actually, replace \left by \left. instead.
EstyProof -> MontanaState
Merge branch 'EstyProof' of github.com:sdoic/webwork-open-problem-library into sdoic-EstyProof
Merge branch 'sdoic-EstyProof'
Fix duplicate problem
Merge branch 'master' of github.com:openwebwork/webwork-open-problem-library
Merge remote-tracking branch 'upstream/master'