<<< native
[ ESub (EGrouped []) (EIdentifier "p")
, ESub (EIdentifier "F") (EIdentifier "q")
, EDelimited
    "("
    ")"
    [ Right (ESub (EIdentifier "a") (ENumber "1"))
    , Right (ESymbol Pun ",")
    , Right (ESymbol Ord "\8230")
    , Right (ESymbol Pun ",")
    , Right (ESub (EIdentifier "a") (EIdentifier "p"))
    , Right (ESymbol Pun ";")
    , Right (ESub (EIdentifier "c") (ENumber "1"))
    , Right (ESymbol Pun ",")
    , Right (ESymbol Ord "\8230")
    , Right (ESymbol Pun ",")
    , Right (ESub (EIdentifier "c") (EIdentifier "q"))
    , Right (ESymbol Pun ";")
    , Right (EIdentifier "z")
    ]
, ESymbol Rel "="
, EUnderover
    True
    (ESymbol Op "\8721")
    (EGrouped [ EIdentifier "n" , ESymbol Rel "=" , ENumber "0" ])
    (ESymbol Ord "\8734")
, EFraction
    NormalFrac
    (EGrouped
       [ ESub
           (EDelimited
              "(" ")" [ Right (ESub (EIdentifier "a") (ENumber "1")) ])
           (EIdentifier "n")
       , ESymbol Ord "\8943"
       , ESub
           (EDelimited
              "(" ")" [ Right (ESub (EIdentifier "a") (EIdentifier "p")) ])
           (EIdentifier "n")
       ])
    (EGrouped
       [ ESub
           (EDelimited
              "(" ")" [ Right (ESub (EIdentifier "c") (ENumber "1")) ])
           (EIdentifier "n")
       , ESymbol Ord "\8943"
       , ESub
           (EDelimited
              "(" ")" [ Right (ESub (EIdentifier "c") (EIdentifier "q")) ])
           (EIdentifier "n")
       ])
, EFraction
    NormalFrac
    (ESuper (EIdentifier "z") (EIdentifier "n"))
    (EGrouped [ EIdentifier "n" , ESymbol Ord "!" ])
]
>>> eqn
{""} sub p F sub q left ( a sub 1 , ... , a sub p ; c sub 1 , ... , c sub q ; z right ) = sum from {n = 0} to inf {{left ( a sub 1 right )} sub n cdots {left ( a sub p right )} sub n} over {{left ( c sub 1 right )} sub n cdots {left ( c sub q right )} sub n} {z sup n} over {n !}