Wondertan

// ProposalData is arbitrary data that Proposers agree on.
//
// Alternative names: consensus.Data, Contract, or can remove alias altogether. 
type ProposalData = []byte

// ValidatorFunc validates the ProposalData and reports back to the Concord
// Q: Verify vs Validate? Quick googling suggests that Validate suits better, but might be wrong.
type ValidatorFunc func(context.Context, ProposalData) (bool, error)

// ProposeFunc builds ProposalData.