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Many parallel applications are designed to conceal parallelism from the user. We investigate a different approach where the user controls many tasks running in parallel. The idea is to let a user accomplish his goal more quickly by trying competing alternatives in parallel (or-parallelism) and by working on subgoals in parallel (and-parallelism). To help the user manage a large number of parallel tasks, the application must provide features to generate many tasks easily, to summarize the state of all tasks, to broadcast commands to related tasks, and to abort tasks that are no longer needed. A parallel interface to an application thus becomes crucial to enhance the user's productivity. We demonstrate this approach using DLP, a parallel, distributed version of the Larch Prover, an interactive theorem prover. DLP supports explicit parallelism and runs on a network of workstations. Users control DLP through a multi-window interface on a bit-map color-display. Many theorem proving problems that would otherwise take considerable user effort to solve have been done with relative ease using DLP.