As Gideon predicted, Lan Wangji does not allow himself to be tripped. He uses the momentum of the shifting in his weight and redirects it -- again, as she predicted, that momentum launches him into the air and into a tidy backward flip. He releases Bichen, which sails behind him and, conveniently, leaves his hands free so that when Gideon gets hold of the hem of his outermost robe, he can briskly tug it free before her pull on him disrupts the arc of his movement. He lands with his boots planted on Bichen, hovering above her.