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The document specifies both .iota and iota. as In general, these procedures return the list whose elements are of the form FROM + i * STEP where 0 <= i < ceiling((TO-FROM)/STEP) (.IOTA) 0 < i <= floor((TO-FROM)/STEP) (IOTA.) While these may be a generalization of APL's iota, what's the rationale for them, vs something like: (iota count) ; start=0, step=1 (iota count start) ; step=1 (iota count start step) ?