Each semantic representation consists of se-mantic units as its tree nodes, where each semantic unit is of the following form: Here m a is used to denote a complete semantic unit, which consists of its semantic type τ a , its function symbol p α , as well as an argument list τ b * (we assume there are at most two arguments for each semantic unit).
each semantic unit can be regarded as a function which takes in other semantics of specific types as arguments, and returns new semantics of a particular type.