add_str(es,⟦⟧);
add_bool(isEmpty)
    ()_check⟦[es]==⟦⟧⟧;
    ()_if⟦[es]≍⟦⟧⟧;
    ()_calc({bool},⟦[es]==⟦⟧⟧);
    ()_test⟦[lens]≍0⟧_lento(lens,⟦[es]⟧);
    ()_is⟦[lens]>0⟧_lento(lens,⟦[es]⟧);
    ()_check⟦[es]===({str},⟦⟧)⟧;
    ()_if⟦[es]≡({str},⟦⟧)⟧;
    ()_calc⟦≣[es]⟧_forme()_forall();
    ()_not⟦[es]≠⟦⟧⟧;
    ()_not()_bool[es];
    ()_empty[es];
    (es)_equal⟦⟦⟧⟧;
;
log_console()_(isEmpty);
log_console()_is(es);  // is not null