public override void Execute(AbstractMachineState state)
{
AMProgram program = (AMProgram)state.Program;
AbstractTerm X0 = ((AbstractTerm)state["X0"]).Dereference();
if (X0.IsConstant || X0.IsStructure || X0.IsList)
{
program.Next();
}
else
{
state.Backtrack();
}
}