Google spreadsheets: how to merge two sheets

Question

Say I have a sheet1 (first image below) and a sheet2 (second image below).

How can I automatically merge two sheets into one as in the third image below? E.g. unchanged cells should be put directly. If a cell is changed, both old and new values should be put to the cell as shown.

Answer 1

=if(Sheet1!A1 = Sheet2!A1, Sheet1!A1, "old:"&Sheet1!A1&" new"&Sheet2!A1) If you copied that into all 4 cells on sheet3, b4 would display "old: fourth new: fifth"