Copy One Parameter Value Into Another Parameter

To Copy the Parameter value passed in the one of the parameter to the below parameters,the concept of :$flex$ need to be used.
For Eg:
In a report there are two parameters,the valueset of the first parameter is xx_file_name is of validation type none.
The value of the above parameter is passed by user from keyboard,to copy the above value to the second parameter in the program.Select the below values
default type:SQL Statement
Default value:Select :$flex$.xx_file_name from dual.
and save the changes you will see the value of the first parameter automatically pouplates to the second parameter.