[ EUnderover
    False (EIdentifier "BASE") (EIdentifier "s") (EIdentifier "t")
, ESymbol Rel "="
, EUnderover
    False
    (EIdentifier "BASE")
    (EGrouped
       [ EPhantom (ENumber "1")
       , EIdentifier "s"
       , EPhantom (ENumber "1")
       ])
    (EGrouped
       [ EPhantom (ENumber "1")
       , EIdentifier "t"
       , EPhantom (ENumber "1")
       ])
]