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must be established before the action is performed);
** postconditions (what is established after the action is performed).

Mathematically, a STRIPS instance is a quadruple , in which each component has the following meaning:

# is a set of conditions (i.e., propositional variables);
# is a set of operators (i.e., actions); each operator is itself a quadruple , each element being a set of conditions. These four sets specify, in order, which conditions must be true for

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