If %EQUAL is used without the optional file_name parameter, then
it returns the value set for the most recent relevant operation.
For the SETLL operation, this function returns '1' if a record
is present whose key or relative record number is equal to the search
argument.
For the LOOKUP operation with the EQ indicator specified, this
function returns '1' if an element is found that exactly matches the
search argument.
If a file name is specified, this function applies to the most
recent SETLL operation for the specified file. This function is allowed
only for files that allow the SETLL operation code.