@Section
   @Title { {"@Common"}, {"@Rump"}, and "@Meld" }
   @Tag { rump }
@Begin
@PP
common.sym @Index { @@Common symbol }
rump.sym @Index { @@Rump symbol }
meld.sym @Index { @@Meld symbol }
The @@Common and @@Rump symbols compare two paragraph objects:
@ID @Code "{ Aardvark, 29 } @Common { Aardvark, 359 }"
If either parameter is not a paragraph object, it is converted into
a single-object paragraph first.  The result of @@Common is the
common prefix of the two paragraphs; that is, those initial objects
which are equal in the two paragraphs.  In the example above, the
result is {@Code "Aardvark,"}.  The result of @@Rump is that part of
the second object which is not included in @@Common; the result of
@ID @Code "{ Aardvark, 29 } @Rump { Aardvark, 359 }"
is {@Code "359"}.
@PP
If the two objects have nothing in common, the result of @@Common will
be an empty object and the result of @@Rump will be the second
object.  If the two objects are identical, the result of @@Common will
be the first object, and the result of @@Rump will be an empty object.
@PP
The only known use for @@Rump and @@Common is to implement merged index
entries (Section {@NumberOf sorted}).
@PP
The @@Meld symbol returns the minimum meld of two paragraphs, that
is the shortest paragraph that contains the two original paragraphs
as subsequences.  For example,
@ID @Code "{ Aardvark , 1 , 2 } @Meld { Aardvark , 2 , 3 }"
produces
@ID { Aardvark , 1 , 2 } @Meld { Aardvark , 2 , 3 }
The result is related to the well-known
longest common substring, in that the meld contains everything not in
the lcs plus one copy of everything in the lcs.  This function is
well-suited to melding complex index entries.  Note that there must be
a non-zero amount of space before each comma, otherwise each will become
part of the preceding word, and, since @@Meld compares the two paragraphs
word by word, the result will be different and less satisfactory.
@End @Section