To the Editor: In her essay "Witness for the Defense" (March 7), Emily Mortimer makes a wonderful and perceptive witness for the defense of Vladimir Nabokov's "Lolita." She does her father proud. Reading her essay, however, reminded me of a much less inspiring witness: Adolf Eichmann, who (according to Hannah Arendt) said to his jailer guard that he found "Lolita" to be "quite an unwholesome book." There is more irony in the world than there is iron.