# S3 method for class 'dd'
+...
# S3 method for class 'dd'
-...
# S3 method for class 'dd'
*...
# S3 method for class 'dd'
...[]
# S3 method for class 'ddl'
`+`(ddl1, ddl2, ...)
# S3 method for class 'ddl'
`-`(ddl1, ddl2, ...)
# S3 method for class 'ddl'
`*`(ddl1, ddl2, ...)