<<< native [ ESuper (EIdentifier "x") (ENumber "1") , ESymbol Bin "+" , ESuper (EIdentifier "x") (EIdentifier "a") , ESymbol Bin "+" , ESuper (EIdentifier "H") (EIdentifier "a") , ESymbol Bin "+" , ESuper (EIdentifier "H") (ENumber "1") ] >>> mml $$x^1+x^a+H^a+H^1$$