anchor.diff:    infoDid: String
     createdPrepaidCards: [PrepaidCard]! @derivedFrom(field: "createdFromDepot")
     bridgedTokens: [BridgeEvent]!       @derivedFrom(field: "depot")
  -}
  -
  -type BridgeEvent @entity {
  -  id: ID!
  -  depot: Depot!
  -  timestamp: BigInt!
  -  supplier: Account!
  -  token: String!
  -  amount: BigInt!
   }
   
   type PrepaidCard @entity {
  
positive.code: type Safe @entity {
    id: ID!                          # safe address
    createdAt: BigInt!               # unix time
    owners: [SafeOwner]!             @derivedFrom(field: "safe")
    sentTokens: [TokenTransfer]!     @derivedFrom(field: "fromSafe")
    receivedTokens: [TokenTransfer]! @derivedFrom(field: "toSafe")
    safeTxns: [SafeTransaction]!     @derivedFrom(field: "safe")
    depot: Depot                     @derivedFrom(field: "safe")
    merchant: MerchantSafe           @derivedFrom(field: "safe")
    prepaidCard: PrepaidCard         @derivedFrom(field: "safe")
  }
  
  type Depot @entity {
  
negative.code:   signatures: Bytes!
  }
  
  # A mapping table is the more performant way to represent many-to-many
  # relationships
  type SafeOwner @entity {
    id: ID!               # Set to safe.id-owner.id
    owner: Account!
    safe: Safe!
  }
  
  type TokenTransfer @entity {
  