Help, help, just on last few but found I may have mucked up top right hand corner as cannot get anything to fit in 12 down. Technical-looking jumbo-jumbo (6-7) I have P?E?D?-S?I?N?E. Is it something science? I thought could have been rocket-science, but then that would mean 8a and 15a wrong as well as 18a. I would much appreciate your help. Thanks in advance.