If two descriptions exist for the same operation but with different numbers of arguments, then the extra arguments are to be treated as optional. For example, this pair of lines:
file-position stream ⇒ position
file-position stream position-spec ⇒ success-p
is operationally equivalent to this line:
file-position stream &optional position-spec ⇒ result
and differs only in that it provides on opportunity to introduce different names for parameter and values for each case. The separated (multi-line) notation is used when an operator is overloaded in such a way that the parameters are used in different ways depending on how many arguments are supplied (e.g., for the function /) or the return values are different in the two cases (e.g., for the function file-position).