  The previous VPT 2020 workshop was organized in honour of Professor Alberto
Pettorossi on the occasion of his academic retirement from Universit\`a di Roma
Tor Vergata. Due to the pandemic the VPT 2020 meeting was cancelled but its
proceeding have already appeared in the EPTCS 320 volume. The joint VPT-20-21
event has subsumed the original programme of VPT 2020 and provided an
opportunity to meet and celebrate the achievements of Professor Alberto
Pettorossi; its programme was further expanded with the newly submitted
presentations for VPT 2021. The aim of the VPT workshop series is to provide a
forum where people from the areas of program transformation and program
verification can fruitfully exchange ideas and gain a deeper understanding of
the interactions between those two fields.
