theorem Th22:
  G is Y_equal-in-column implies h_strip(G,width G) = { |[r,s]| :
  G*(1,width G)`2 <= s }
proof
  0 <> len G by MATRIX_0:def 10;
  then
A1: 1 <= len G by NAT_1:14;
  assume G is Y_equal-in-column;
  hence thesis by A1,GOBOARD5:6;
end;
