<<< native [ EUnderover False (EIdentifier "BASE") (EIdentifier "under") (EIdentifier "over") , ESymbol Rel "=" , EOver False (EUnder False (EIdentifier "BASE") (EIdentifier "under")) (EIdentifier "over") ] >>> mml $$\underset{\mathrm{under}}{\overset{\mathrm{over}}{\mathrm{BASE}}}=\stackrel{\mathrm{over}}{\underset{\mathrm{under}}{\mathrm{BASE}}}$$