let i be Element of NAT ; :: thesis: for G being Matrix of (TOP-REAL 2) st not G is empty-yielding & G is Y_equal-in-column & 1 <= i & i <= len G holds
h_strip G,(width G) = { |[r,s]| where r, s is Real : (G * i,(width G)) `2 <= s }
let G be Matrix of (TOP-REAL 2); :: thesis: ( not G is empty-yielding & G is Y_equal-in-column & 1 <= i & i <= len G implies h_strip G,(width G) = { |[r,s]| where r, s is Real : (G * i,(width G)) `2 <= s } )
assume that
A1: ( not G is empty-yielding & G is Y_equal-in-column ) and
A2: 1 <= i and
A3: i <= len G ; :: thesis: h_strip G,(width G) = { |[r,s]| where r, s is Real : (G * i,(width G)) `2 <= s }
width G <> 0 by A1, GOBOARD1:def 5;
then 1 <= width G by NAT_1:14;
then (G * i,(width G)) `2 = (G * 1,(width G)) `2 by A1, A2, A3, Th2;
hence h_strip G,(width G) = { |[r,s]| where r, s is Real : (G * i,(width G)) `2 <= s } by Def2; :: thesis: verum