But such questions are, finally, rhetorical. They are effectively sidelined by Os Gemeos’s delirious patterning and cartoony drawing — and by the palpable civic chutzpah the piece embodies. (Just think of all the draining meetings with mayoral staffers, law enforcement officials, museum curators, and corporate sponsors required to pull off a commission like this! No wonder fans of street art look back with nostalgia upon a putative golden age!)

The ICA show adds depth and complexity to our view of these artists. A few of the works in it are a little on the twee side. But they make it easy to see why these twins are now, as Alonzo puts it, “the face of the Brazilian graffiti movement.”

The best of the works manage to be both ironically knowing and sincerely openhearted. They are full of trompe l’oeil effects and other shifts in visual register, from stenciled patterning to conventional perspective and even relief carving.

There is a children’s picture book quality to much of what they do — an impression cemented by their signature yellow, skinny-limbed protagonists. And one could perhaps argue that the fundamental requirements of successful street art (recognizable style, ubiquity, repetition) can feel like fetters on genuine creative expression: that these things should be, if anything, byproducts, not explicit ambitions.

But what is exciting about Os Gemeos is that, starting gleefully from within the parameters of street art, they are constantly busting out of those parameters.