Lm1:
for n, i being Nat st i in Seg n holds
(n + 1) - i in Seg n
Lm2:
for n, i, j being Nat st [i,j] in [:(Seg n),(Seg n):] holds
( (n + 1) - j in Seg n & (n + 1) - i in Seg n )
Lm3:
for n, i, j being Nat st i in Seg n & j in Seg n & i + j <> n + 1 holds
((i + j) - 1) mod n in Seg n
Lm4:
for n, i, j being Nat st [i,j] in [:(Seg n),(Seg n):] & i + j <> n + 1 holds
((i + j) - 1) mod n in Seg n