cospan.test

<<< tex
B \xrightarrow[f]{} A \xleftarrow[f]{} C


>>> native
[ EIdentifier "B"
, EUnderover
    False (ESymbol Op "\8594") (EIdentifier "f") (EGrouped [])
, EIdentifier "A"
, EUnderover
    False (ESymbol Op "\8592") (EIdentifier "f") (EGrouped [])
, EIdentifier "C"
]