my @remaining = grep {defined} split /[+-]{2,}/, $righteq;
  # fixed 2nd arg error
##</code><code>##

my @remaining = grep {defined}
                      split /
                            (e\^\(t\+-(\d+\.?\d*|\.\d+)\))
                                   # the special, captured
                            |      # or else
                            [+-]+  # filler, not captured
                            /x,
                            $righteq;