theorem Th31: :: GOBOARD6:31

for i, j being Nat
for G being Go-board st 1 <= i & i + 1 <= len G & 1 <= j & j + 1 <= width G holds
(1 / 2) * ((G * (i,j)) + (G * ((i + 1),(j + 1)))) in Int (cell (G,i,j))