Triphenylphosphine can be used to open epoxides via nucleophilic substitution. The initial substitution product (a betaine) quickly cyclizes to a 4-membered ring (oxaphosphetane) that collapses to triphenylphosphine oxide and an alkene. Draw the arrow-pushing mechanism for the reaction of trans-3,4-epoxyhexane and triphenylphosphine to produce hex-3-ene. Identify the specific stereoisomer of the product.