an class="hspace">&nbsp;</span>&rarr;<span class="hspace">&nbsp;</span><span class="RktPn">(</span><span class="RktSym"><a href="http://docs.racket-lang.org/reference/data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._one-of%2Fc%29%29" class="RktValLink" data-pltdoc="x">one-of/c</a></span><span class="hspace">&nbsp;</span><span class="RktVal">'</span><span class="RktVal">ok</span><span class="hspace">&nbsp;</span><span class="RktVal">'</span><span class="RktVal">wrong-hierarc