It is very unlikely that any piece of text will be annotated with more than one non-operator or with more than one operator, 2 though it is common for text to be anno-   tated with one non-operator and one operator (see Figure 1).
we can use two softmaxes, one for non-operators and one for operators, and the 2-Softmax model thus can produce 0, 1, or 2 labels per input.