found a tool, called a "toe board saw" (?). Small circular saw that braces itself against the toe board and cuts through the plywood. Works great. Watch out for mounting screws for cabinets though! Bought a new blade. Also used a roofing shovel to pry up the plywood. The builders must have had stock in glue and staples. Glue strips every 3" and staples in columes spaced about 3" apart and rows 1.5" apart!