SELECT
    a != b, -- Space is part of physical JSON content. Despite equal logical content, values are treated as not equal.
    c != d, -- Same.
    c[0] = d[0], -- Equality because space was removed from physical content of fields:
    a = c[0], -- Indeed, field is equal to empty list without space...
    b != c[0], -- ... but different from empty list with space.
FROM (
    SELECT
        '[]'::JSON AS a,
        '[ ]'::JSON AS b,
        '[[]]'::JSON AS c,
        '[[ ]]'::JSON AS d
    );