<<< native [ EUnder False (EIdentifier "middle") (EIdentifier "bottom") , ESymbol Rel "=" , EUnderover False (EIdentifier "middle") (EIdentifier "bottom") (EPhantom (EIdentifier "fail")) ] >>> mml $$\underset{\mathrm{bottom}}{\mathrm{middle}}=\underset{\mathrm{bottom}}{\overset{\phantom{\mathrm{fail}}}{\mathrm{middle}}}$$