index = repLitLeft.indexOf(var);
// (x,<a>),(y,x) => (x,<a>),(y,<a>)
if (index > -1) {
final Variable var2 = repVarLeft.get(i);
repVar_new.removeSubstitution(var2, var);
repLit_new.addSubstitution(var2, repLitRight.get(index));
}
}
final LinkedList<BasicOperator> pres = (LinkedList<BasicOperator>) repLit
.getPrecedingOperators();