KIF expression is either a word or a list of expressions.
(First (First ?Expr))
(<=> (Expression ?Expr) (Or (Word ?Expr) (And (List ?Expr) (Forall (?Subexpr) (=> (Item ?Subexpr ?Expr) (Expression ?Subexpr))))))
(Or (Word ?Expr) (And (List ?Expr) (Forall (?Subexpr) (=> (Item ?Subexpr ?Expr) (Expression ?Subexpr)))))
(Or (Word ?Expr) (And (List ?Expr) (Forall (?Subexpr) (=> (Item ?Subexpr ?Expr) (Expression ?Subexpr))))) (<=> (Expression ?Expr) (Or (Word ?Expr) (And (List ?Expr) (Forall (?Subexpr) (=> (Item ?Subexpr ?Expr) (Expression ?Subexpr)))))) (Alias Term Expression) (<=> (Quoterm ?Expr) (And (Term ?Expr) (List ?Expr) (= (First ?Expr) (Quote Quote)) (Expression (First (First ?Expr)))))