let G be V9() Matrix of (TOP-REAL 2); :: thesis: ( G is Y_equal-in-column implies h_strip G,0 = { |[r,s]| where r, s is Real : s <= (G * 1,1) `2 } )
0 <> len G by GOBOARD1:def 5;
then A1: 1 <= len G by NAT_1:14;
assume G is Y_equal-in-column ; :: thesis: h_strip G,0 = { |[r,s]| where r, s is Real : s <= (G * 1,1) `2 }
hence h_strip G,0 = { |[r,s]| where r, s is Real : s <= (G * 1,1) `2 } by A1, GOBOARD5:8; :: thesis: verum