<<< native [ EUnder False (EIdentifier "BASE") (EIdentifier "x") , ESymbol Rel "=" , EUnder False (EIdentifier "BASE") (EGrouped [ EPhantom (ENumber "1") , EIdentifier "x" , EPhantom (ENumber "1") ]) ] >>> tex \underset{x}{BASE} = \underset{\phantom{1}x\phantom{1}}{BASE}