cospan.test

<<< native
[ EIdentifier "B"
, EUnderover
    False (ESymbol Op "\8594") (EIdentifier "f") (EGrouped [])
, EIdentifier "A"
, EUnderover
    False (ESymbol Op "\8592") (EIdentifier "f") (EGrouped [])
, EIdentifier "C"
]
>>> tex
B\xrightarrow[{f}]{}A\xleftarrow[{f}]{}C