ABSTRACT
The sequents considered so far, having sets as their left sides, I shall call s - sequents. I now shall present calculi which employ sequents, the left sides of which are sequences. So a t -sequent M = } u shall be a pair consisting of a (possibly em pty) sequence M of formulas together w ith a formula u ; the prefix t will be om itted if no am biguity can arise. In order to improve readability, I som etim es shall write ▲ v for M = $ v w ith an em pty M .
