fact: Definition must {A} (o: option A) : if o then A else unit := match o with | Some a => a | None => tt end.
imports: BinNat Coq.Lists.List Bedrock.Word Fiat.Common.EnumType Fiat.Narcissus.Formats.ByteBuffer Fiat.Narcissus.Examples.NetworkStack.IPv4Header Fiat.Narcissus.Examples.NetworkStack.UDP_Packet Fiat.Narcissus.Examples.NetworkStack.TCP_Packet