The idea of a truth maintenance system ( TMS) grew out of dependency-directed backtracking.

Given a set of boolean variables (or assumptions) &Sigma and a set of boolean constraints &Gamma , the general problem is to find a set of assignments to the variables that satisfies all the constraints.

Applications:

• Solve search problems, e.g., schedule meetings so that everyone can attend.

• Determine what derived conclusions are still true when some facts change.

• Determine what part failures could have caused a machine to fail.

Constraints could be expressed as:

• A `digital electronics' network.

• A set of IN and OUT nodes that must be satisfied for a node to be true ( IN).

• Logical relationships among boolean variables.

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