I came across the Alfa proof language recently (precursor to Epigram and Agda). Had this neat natural deduction editor: http://www.cse.chalmers.se/~hallgren/Alf

I came across the Alfa proof language recently (precursor to Epigram and Agda). Had this neat natural deduction editor: http://www.cse.chalmers.se/~hallgren/Alfa/Tutorial/ndstyle.html http://www.cse.chalmers.se/~hallgren/Alfa/Tutorial/ndstyle.h...