Consider binary strings of length 6. The schema codice_1 describes the set of all strings of length 6 with 1's at positions 1, 3 and 6 and a 0 at position 4. The * is a wildcard symbol, which means that positions 2 and 5 can have a value of either 1 or 0. The "order of a schema" formula_1 is defined as the number of fixed positions in the template, while the "defining length" formula_2 is the distance between the first and last specific positions. The order of codice_1 is 4 and its defining length is 5. The "fitness of a schema" is the average fitness of all strings matching the schema. The fitness of a string is a measure of the value of the encoded problem solution, as computed by a problem-specific evaluation function. Using the established methods and genetic operators of genetic algorithms, the schema theorem states that short, low-order schemata with above-average fitness increase exponentially in successive generations. Expressed as an equation: