Show the curved-arrow mechanism for the Claisen condensation of ethyl ethanoate treated with ethoxide ion. Include all formal charges and nonbonding electrons. In each step, draw only the species that react in that step. If an enolate resonance form is possible, draw only the carbanionic form. If a CHx group is being deprotonated, draw all H\'s on the reacting site. Tip: always omit ethanol byproducts.