[twig] IF a == true OR b == true statement

I can't find a way to have TWIG interpret the following conditional statement:

{% if a == true or b == true %}
do stuff
{% endif %}

Am I missing something or it's not possible?

Comparison expressions should each be in their own brackets:

{% if (a == 'foo') or (b == 'bar') %}
    ...
{% endif %}

Alternative if you are inspecting a single variable and a number of possible values:

{% if a in ['foo', 'bar', 'qux'] %}
    ...
{% endif %}