toFType (FApp c [_,ity])
    | c == sUN "C_IntT" = FArith (toAType ity)
    | c == sUN "C_FnT" = toFunType ity
toFType (FApp c [_,ity])
    | c == sUN "C_IntT" = FArith (toAType ity)
    | c == sUN "C_FnT" = toFunType ity
toFType (FApp c [_,ity])
    | c == sUN "C_IntT" = FArith (toAType ity)
    | c == sUN "C_FnT" = toFunType ity