abstract = "Simple enhancements to the standard population
operators of mutation and crossover, using Abstract
Expression Grammars, are investigated. In previous
works, Abstract Expression Grammars have been used to
integrate Genetic Algorithms, Genetic Programming,
Swarm Intelligence, and Differential Evolution, into a
seamlessly unified approach to symbolic regression. In
this work, the potential for Abstract Expression
Grammars to have a direct impact on the classic Genetic
Programming mutation and crossover operators is
demonstrated. The features of abstract expression
grammars are explored, details of abstract mutation and
crossover are provided, and the beneficial effects of
abstract mutation and crossover are tested with several
published nonlinear regression problems.",