Editing Surreal number (section)

===Notation===
In the context of surreal numbers, an [[ordered pair]] of sets {{mvar|L}} and {{mvar|R}}, which is written as {{math|(''L'', ''R'')}} in many other mathematical contexts, is instead written {{math|{{mset| ''L'' {{!}} ''R'' }}}} including the extra space adjacent to each brace.  When a set is empty, it is often simply omitted.  When a set is explicitly described by its elements, the pair of braces that encloses the list of elements is often omitted.  When a union of sets is taken, the operator that represents that is often a comma.  For example, instead of {{math|(''L''{{sub|1}} ∪ ''L''{{sub|2}} ∪ {{mset|0, 1, 2}}, ∅)}}, which is common notation in other contexts, we typically write {{math|{{mset| ''L''{{sub|1}}, ''L''{{sub|2}}, 0, 1, 2 {{!}} }}}}.