I think that you misunderstand what really an input is. The symbolic representation is used to encode the real inputs which are assignments to the boolean input variables. Thus, having two input variables like a and b, we have the four inputs {a=0,b=0}, {a=0,b=1}, {a=1,b=0}, {a=1,b=1}. If in one state there is a transition labelled with !a|b then this transition can be taken for inputs {a=0,b=0}, {a=0,b=1}, {a=1,b=1}, and if there is another transition labelled with a&b, it can be taken for input {a=1,b=1}. Hence, for the input {a=1,b=1}, both transitions can be taken. For the subset of breakpoint construction, we considered explicit encodings of the automata, and not the symbolic ones. There are also algorithms for the determinization of the symbolic versions, but that is more difficult (and also implemented in the teaching tools for translating LTL to deterministic automata). The principles behind are the same, but the implementation is more involved for the symbolic versions.