logical operators

iter.sml

val rec iter = fn 0 => (fn f => fn x => x) | n => (fn f => fn x => (f o (iter (n-1) f)) x); 

logic.sml

fun conj x y = case (x,y) of (true, true) => true | _ => false;

fun disj x y = case (x,y) of (true, _) => true |  (_, true) => true | _ => false;

fun impl x y = case (x,y) of (false, _) => true | (true, true) => true | _ => false; 

fun equiv x y = case (x,y) of (false, false) => true | (true, true) => true | _ => false; 

semifac.sml

fun semifac n = reduce ((op * ), 1, 1, (n div 2), (fn x => 2 * x + n mod 2));