Controlling the Control

• Sometimes the programmer knows quite a bit
• E.g., some goal may not be useful until some condition (as the instantiation of a variable) holds
• delay Goal until Condition the execution of Goal is delayed until Condition holds
  • Needs fairly good knowledge of the constraint system
  • Also widely available in Prolog systems
• Cut: do not take certain parts of the search tree into account
• We may know that, at some point, the current path is the right one
• If we do not need more solutions, we can cut the search in alternative branches
• Also inherited from Prolog