Selection-screen functionality

Hi,

I have 2 questions regarding selection-screens:

1. I have 2 select-options like this in my selection-screen:

Matnr: s_matnr

Vendor: s_lifnr

How can I make a check that if Matnr is filled then Vendor has to be filled as well and vice versa ?

2. I want to take the interval of data from a select-option and create the records in an internal table:

example

Contract no: From 45000000 To 45000025

All the records that are contracts (document cat. = K) from that interval have to be appended to an internal table.