Calkin–Wilf tree
... that one can list every positive rational number without repetition by breadth-first traversal of the Calkin–Wilf tree?
... that one can list every <a class="mw-redirect" href="./Positive_number" id="mwEnE" rel="mw:WikiLink" title="Positive number">positive</a> <a href="./Rational_number" id="mwEnI" rel="mw:WikiLink" title="Rational number">rational number</a> without repetition by <a href="./Breadth-first_search" id="mwEnM" rel="mw:WikiLink" title="Breadth-first search">breadth-first traversal</a> of the <b id="mwEnQ"><a href="./Calkin–Wilf_tree" id="mwEnU" rel="mw:WikiLink" title="Calkin–Wilf tree">Calkin–Wilf tree</a></b>?