theorem :: GOBOARD7:48
for i, j, k being Nat
for f being constant standard special_circular_sequence st 1 <= i & i <= len (GoB f) & 1 <= j & j + 1 < width (GoB f) & 1 <= k & k + 1 < len f & LSeg (((GoB f) * (i,j)),((GoB f) * (i,(j + 1)))) = LSeg (f,k) & LSeg (((GoB f) * (i,(j + 1))),((GoB f) * (i,(j + 2)))) = LSeg (f,(k + 1)) holds
( f /. k = (GoB f) * (i,j) & f /. (k + 1) = (GoB f) * (i,(j + 1)) & f /. (k + 2) = (GoB f) * (i,(j + 2)) )