FIGURE 26.
IOTA Tangle graph with milestone transactions m 0 and m 1. Assume that transactions t 1 and t 2 double spend the same IOTA coins. As m 1 indirectly confirms t 1, all transactions (marked with a cross sign) that confirm t 2 are building on an invalid subgraph. As a result, these transactions will not be used as tips in future transactions. If a transaction such as Self1 is not confirmed in time, we can create a new zero value transaction Self2 that confirms Self1. New transactions will use Self2 as a tip so that Self1 will be indirectly confirmed by them. Consequently, we hope that Self1 will be indirectly confirmed by a future milestone transaction