theorem Th19:
  G is X_equal-in-line implies v_strip(G,len G) = { |[r,s]| : G*(
  len G,1)`1 <= r }
proof
  0 <> width G by MATRIX_0:def 10;
  then
A1: 1 <= width G by NAT_1:14;
  assume G is X_equal-in-line;
  hence thesis by A1,GOBOARD5:9;
end;
