Simon Tatham Bridges

You have a set of islands distributed across the playing area. Each island contains a number. Your aim is to Connect the islands together with bridges, in such a way that:* Bridges run horizontally or vertically.* The number of bridges terminating at any island is equal to the number written in that island.* Two bridges may run in parallel Between the same two islands, but no more than two may do so.* No bridge crosses another bridge.* All the islands are connected together.There are some configurable alternative modes, which involve changing the parallel-bridge limit to something other than 2, and introducing the additional constraint that no sequence of bridges may form a loop from one island back to the same island. The rules stated above are the default ones.