let G be Go-board; :: thesis: for i, j, k, j1, k1 being Nat st 1 <= i & i <= width G & 1 <= j & j <= j1 & j1 <= k1 & k1 <= k & k <= len G holds
LSeg ((G * (j1,i)),(G * (k1,i))) c= LSeg ((G * (j,i)),(G * (k,i)))

let i, j, k, j1, k1 be Nat; :: thesis: ( 1 <= i & i <= width G & 1 <= j & j <= j1 & j1 <= k1 & k1 <= k & k <= len G implies LSeg ((G * (j1,i)),(G * (k1,i))) c= LSeg ((G * (j,i)),(G * (k,i))) )
assume that
A1: 1 <= i and
A2: i <= width G and
A3: 1 <= j and
A4: j <= j1 and
A5: j1 <= k1 and
A6: k1 <= k and
A7: k <= len G ; :: thesis: LSeg ((G * (j1,i)),(G * (k1,i))) c= LSeg ((G * (j,i)),(G * (k,i)))
A8: j1 <= k by ;
j <= k1 by ;
then A9: 1 <= k1 by ;
then A10: (G * (k1,i)) `1 <= (G * (k,i)) `1 by ;
A11: 1 <= j1 by ;
1 <= j1 by ;
then A12: 1 <= k by ;
A13: k1 <= len G by ;
j <= k1 by ;
then A14: j <= len G by ;
then (G * (j,i)) `2 = (G * (1,i)) `2 by
.= (G * (k,i)) `2 by ;
then A15: LSeg ((G * (j,i)),(G * (k,i))) is horizontal by SPPOL_1:15;
j1 <= k by ;
then A16: j1 <= len G by ;
then A17: (G * (j,i)) `1 <= (G * (j1,i)) `1 by ;
A18: k1 <= len G by ;
then A19: (G * (j1,i)) `1 <= (G * (k1,i)) `1 by ;
(G * (j1,i)) `2 = (G * (1,i)) `2 by
.= (G * (k1,i)) `2 by ;
then A20: LSeg ((G * (j1,i)),(G * (k1,i))) is horizontal by SPPOL_1:15;
(G * (j,i)) `2 = (G * (1,i)) `2 by
.= (G * (j1,i)) `2 by ;
hence LSeg ((G * (j1,i)),(G * (k1,i))) c= LSeg ((G * (j,i)),(G * (k,i))) by ; :: thesis: verum